diff --git a/example/src/i18n.js b/example/src/i18n.js
index 349adb7..700dc2d 100644
--- a/example/src/i18n.js
+++ b/example/src/i18n.js
@@ -1,7 +1,18 @@
-import { register, setFallbackLocale } from 'svelte-i18n'
+import { register, configure } from 'svelte-i18n'
+
+configure({
+  fallbackLocale: 'en',
+  initialLocale: {
+    navigator: true,
+  },
+  formats: {
+    number: {
+      BRL: { style: 'currency', currency: 'BRL' },
+    },
+  },
+  loadingDelay: 200,
+})
 
 register('en', () => import('../messages/en.json'))
 register('pt-BR', () => import('../messages/pt-BR.json'))
 register('es-ES', () => import('../messages/es-ES.json'))
-
-setFallbackLocale('en')
diff --git a/example/src/routes/_layout.svelte b/example/src/routes/_layout.svelte
index 7bf9195..bc62040 100644
--- a/example/src/routes/_layout.svelte
+++ b/example/src/routes/_layout.svelte
@@ -1,12 +1,8 @@
 <script context="module">
-  import { isLoading, setInitialLocale } from 'svelte-i18n'
+  import { isLoading, waitLocale } from 'svelte-i18n'
 
   export async function preload() {
-    return setInitialLocale({
-      fallback: 'en',
-      // navigator: true,
-      search: 'lang'
-    })
+    return waitLocale()
   }
 </script>
 
diff --git a/src/client/configs.ts b/src/client/configs.ts
new file mode 100644
index 0000000..83e575a
--- /dev/null
+++ b/src/client/configs.ts
@@ -0,0 +1,67 @@
+import { getClientLocale } from './includes/utils'
+import { ConfigureOptions } from './types'
+import { $locale } from './stores/locale'
+
+let fallbackLocale: string = null
+let loadingDelay = 200
+const formats: any = {
+  number: {
+    scientific: { notation: 'scientific' },
+    engineering: { notation: 'engineering' },
+    compactLong: { notation: 'compact', compactDisplay: 'long' },
+    compactShort: { notation: 'compact', compactDisplay: 'short' },
+  },
+  date: {
+    short: { month: 'numeric', day: 'numeric', year: '2-digit' },
+    medium: { month: 'short', day: 'numeric', year: 'numeric' },
+    long: { month: 'long', day: 'numeric', year: 'numeric' },
+    full: { weekday: 'long', month: 'long', day: 'numeric', year: 'numeric' },
+  },
+  time: {
+    short: { hour: 'numeric', minute: 'numeric' },
+    medium: { hour: 'numeric', minute: 'numeric', second: 'numeric' },
+    long: {
+      hour: 'numeric',
+      minute: 'numeric',
+      second: 'numeric',
+      timeZoneName: 'short',
+    },
+    full: {
+      hour: 'numeric',
+      minute: 'numeric',
+      second: 'numeric',
+      timeZoneName: 'short',
+    },
+  },
+}
+
+export function getFallbackLocale() {
+  return fallbackLocale
+}
+
+export function getLoadingDelay() {
+  return loadingDelay
+}
+
+export function getFormats() {
+  return formats
+}
+
+export function configure(opts: ConfigureOptions) {
+  fallbackLocale = opts.fallbackLocale
+
+  if (opts.initialLocale) {
+    $locale.set(getClientLocale(opts.initialLocale) || fallbackLocale)
+  } else {
+    $locale.set(fallbackLocale)
+  }
+
+  if (opts.formats) {
+    if ('number' in opts.formats)
+      Object.assign(formats.number, opts.formats.number)
+    if ('date' in opts.formats) Object.assign(formats.date, opts.formats.date)
+    if ('time' in opts.formats) Object.assign(formats.time, opts.formats.time)
+  }
+
+  if (loadingDelay != null) loadingDelay = loadingDelay
+}
diff --git a/src/client/includes/formats.ts b/src/client/includes/formatters.ts
similarity index 66%
rename from src/client/includes/formats.ts
rename to src/client/includes/formatters.ts
index 93029ba..0a8a40d 100644
--- a/src/client/includes/formats.ts
+++ b/src/client/includes/formatters.ts
@@ -1,32 +1,17 @@
-import IntlMessageFormat, { Formats } from 'intl-messageformat'
+import IntlMessageFormat from 'intl-messageformat'
 import memoize from 'fast-memoize'
 
 import { MemoizedIntlFormatter } from '../types'
 import { getCurrentLocale } from '../stores/locale'
-
-export const customFormats: any = {
-  number: {
-    scientific: { notation: 'scientific' },
-    engineering: { notation: 'engineering' },
-    compactLong: { notation: 'compact', compactDisplay: 'long' },
-    compactShort: { notation: 'compact', compactDisplay: 'short' },
-  },
-  date: {},
-  time: {},
-}
-
-export function addCustomFormats(formats: Partial<Formats>) {
-  if ('number' in formats) Object.assign(customFormats.number, formats.number)
-  if ('date' in formats) Object.assign(customFormats.date, formats.date)
-  if ('time' in formats) Object.assign(customFormats.time, formats.time)
-}
+import { getFormats } from '../configs'
 
 const getIntlFormatterOptions = (
   type: 'time' | 'number' | 'date',
   name: string
 ): any => {
-  if (type in customFormats && name in customFormats[type]) {
-    return customFormats[type][name]
+  const formats = getFormats()
+  if (type in formats && name in formats[type]) {
+    return formats[type][name]
   }
 
   if (
@@ -77,5 +62,5 @@ export const getTimeFormatter: MemoizedIntlFormatter<
 
 export const getMessageFormatter = memoize(
   (message: string, locale: string) =>
-    new IntlMessageFormat(message, locale, customFormats)
+    new IntlMessageFormat(message, locale, getFormats())
 )
diff --git a/src/client/includes/loaderQueue.ts b/src/client/includes/loaderQueue.ts
index 37e0d97..710aa8a 100644
--- a/src/client/includes/loaderQueue.ts
+++ b/src/client/includes/loaderQueue.ts
@@ -4,8 +4,9 @@ import {
   $dictionary,
   addMessages,
 } from '../stores/dictionary'
-import { getCurrentLocale, getFallbacksOf } from '../stores/locale'
+import { getCurrentLocale, getRelatedLocalesOf } from '../stores/locale'
 import { $isLoading } from '../stores/loading'
+import { getLoadingDelay } from '../configs'
 
 type Queue = Set<MessagesLoader>
 const loaderQueue: Record<string, Queue> = {}
@@ -23,7 +24,7 @@ function getLocaleQueue(locale: string) {
 }
 
 function getLocalesQueues(locale: string) {
-  return getFallbacksOf(locale)
+  return getRelatedLocalesOf(locale)
     .reverse()
     .map<[string, MessagesLoader[]]>(localeItem => {
       const queue = getLocaleQueue(localeItem)
@@ -33,7 +34,7 @@ function getLocalesQueues(locale: string) {
 }
 
 export function hasLocaleQueue(locale: string) {
-  return getFallbacksOf(locale)
+  return getRelatedLocalesOf(locale)
     .reverse()
     .some(getLocaleQueue)
 }
@@ -45,14 +46,14 @@ export function addLoaderToQueue(locale: string, loader: MessagesLoader) {
 const activeLocaleFlushes: { [key: string]: Promise<void> } = {}
 export async function flushQueue(locale: string = getCurrentLocale()) {
   if (!hasLocaleQueue(locale)) return
-  if (activeLocaleFlushes[locale]) return activeLocaleFlushes[locale]
+  if (locale in activeLocaleFlushes) return activeLocaleFlushes[locale]
 
   // get queue of XX-YY and XX locales
   const queues = getLocalesQueues(locale)
   if (queues.length === 0) return
 
   removeLocaleFromQueue(locale)
-  const loadingDelay = setTimeout(() => $isLoading.set(true), 200)
+  const loadingDelay = setTimeout(() => $isLoading.set(true), getLoadingDelay())
 
   // TODO what happens if some loader fails
   activeLocaleFlushes[locale] = Promise.all(
diff --git a/src/client/includes/utils.ts b/src/client/includes/utils.ts
index e3335d1..0256125 100644
--- a/src/client/includes/utils.ts
+++ b/src/client/includes/utils.ts
@@ -39,8 +39,6 @@ export const getClientLocale = ({
   search,
   pathname,
   hostname,
-  default: defaultLocale,
-  fallback = defaultLocale,
 }: GetClientLocaleOptions) => {
   let locale
 
@@ -78,5 +76,5 @@ export const getClientLocale = ({
     if (locale) return locale
   }
 
-  return fallback
+  return null
 }
diff --git a/src/client/index.ts b/src/client/index.ts
index ea022dc..2f94c4f 100644
--- a/src/client/index.ts
+++ b/src/client/index.ts
@@ -1,5 +1,3 @@
-import merge from 'deepmerge'
-
 import { MessageObject } from './types'
 
 // defineMessages allow us to define and extract dynamic message ids
@@ -7,11 +5,8 @@ export function defineMessages(i: Record<string, MessageObject>) {
   return i
 }
 
-export {
-  $locale as locale,
-  setInitialLocale,
-  setFallbackLocale,
-} from './stores/locale'
+export { configure } from './configs'
+export { $locale as locale } from './stores/locale'
 export {
   $dictionary as dictionary,
   $locales as locales,
@@ -21,12 +16,7 @@ export { $isLoading as isLoading } from './stores/loading'
 export { $format as format, $format as _, $format as t } from './stores/format'
 
 // utilities
-export { merge }
-export { customFormats, addCustomFormats } from './includes/formats'
 export {
   flushQueue as waitLocale,
   registerLocaleLoader as register,
 } from './includes/loaderQueue'
-
-// @deprecated
-export { getClientLocale } from './includes/utils'
diff --git a/src/client/stores/format.ts b/src/client/stores/format.ts
index ff18ea6..f85ee70 100644
--- a/src/client/stores/format.ts
+++ b/src/client/stores/format.ts
@@ -9,10 +9,10 @@ import {
   getTimeFormatter,
   getDateFormatter,
   getNumberFormatter,
-} from '../includes/formats'
+} from '../includes/formatters'
 
 import { $dictionary } from './dictionary'
-import { getCurrentLocale, getFallbacksOf, $locale } from './locale'
+import { getCurrentLocale, getRelatedLocalesOf, $locale } from './locale'
 
 const formatMessage: Formatter = (id, options = {}) => {
   if (typeof id === 'object') {
@@ -32,7 +32,7 @@ const formatMessage: Formatter = (id, options = {}) => {
 
   if (!message) {
     console.warn(
-      `[svelte-i18n] The message "${id}" was not found in "${getFallbacksOf(
+      `[svelte-i18n] The message "${id}" was not found in "${getRelatedLocalesOf(
         locale
       ).join('", "')}". ${
         hasLocaleQueue(getCurrentLocale())
diff --git a/src/client/stores/locale.ts b/src/client/stores/locale.ts
index ccb65ef..b4822ee 100644
--- a/src/client/stores/locale.ts
+++ b/src/client/stores/locale.ts
@@ -5,19 +5,11 @@ import { getClientLocale } from '../includes/utils'
 import { GetClientLocaleOptions } from '../types'
 
 import { getClosestAvailableLocale } from './dictionary'
+import { setFallbackLocale, getFallbackLocale } from '../configs'
 
-let fallbackLocale: string = null
 let current: string
 const $locale = writable(null)
 
-export function getFallbackLocale() {
-  return fallbackLocale
-}
-
-export function setFallbackLocale(locale: string) {
-  fallbackLocale = locale
-}
-
 export function isFallbackLocaleOf(localeA: string, localeB: string) {
   return localeB.indexOf(localeA) === 0 && localeA !== localeB
 }
@@ -33,19 +25,19 @@ export function isRelatedLocale(localeA: string, localeB: string) {
 export function getFallbackOf(locale: string) {
   const index = locale.lastIndexOf('-')
   if (index > 0) return locale.slice(0, index)
-  if (fallbackLocale && !isRelatedLocale(locale, fallbackLocale)) {
-    return fallbackLocale
+  if (getFallbackLocale() && !isRelatedLocale(locale, getFallbackLocale())) {
+    return getFallbackLocale()
   }
   return null
 }
 
-export function getFallbacksOf(locale: string): string[] {
+export function getRelatedLocalesOf(locale: string): string[] {
   const locales = locale
     .split('-')
     .map((_, i, arr) => arr.slice(0, i + 1).join('-'))
 
-  if (fallbackLocale && !isRelatedLocale(locale, fallbackLocale)) {
-    return locales.concat(getFallbacksOf(fallbackLocale))
+  if (getFallbackLocale() && !isRelatedLocale(locale, getFallbackLocale())) {
+    return locales.concat(getRelatedLocalesOf(getFallbackLocale()))
   }
   return locales
 }
@@ -54,13 +46,6 @@ export function getCurrentLocale() {
   return current
 }
 
-export function setInitialLocale(options: GetClientLocaleOptions) {
-  if (typeof options.fallback === 'string') {
-    setFallbackLocale(options.fallback)
-  }
-  return $locale.set(getClientLocale(options))
-}
-
 $locale.subscribe((newLocale: string) => {
   current = newLocale
 
diff --git a/src/client/types/index.ts b/src/client/types/index.ts
index e3bdcf4..edf8638 100644
--- a/src/client/types/index.ts
+++ b/src/client/types/index.ts
@@ -1,3 +1,5 @@
+import { Formats } from 'intl-messageformat'
+
 export interface Dictionary {
   [key: string]: string | string[] | Dictionary | Dictionary[]
 }
@@ -50,8 +52,14 @@ export interface GetClientLocaleOptions {
   navigator?: boolean
   hash?: string | RegExp
   search?: string | RegExp
-  fallback?: string
   default?: string
   pathname?: RegExp
   hostname?: RegExp
 }
+
+export interface ConfigureOptions {
+  fallbackLocale: string
+  initialLocale?: GetClientLocaleOptions
+  formats?: Partial<Formats>
+  loadingDelay?: number
+}
diff --git a/test/client/locale.test.ts b/test/client/locale.test.ts
index d5e5d89..f85eff0 100644
--- a/test/client/locale.test.ts
+++ b/test/client/locale.test.ts
@@ -1,23 +1,22 @@
+import { get } from 'svelte/store'
+
 import {
-  getFallbackLocale,
-  setFallbackLocale,
   isFallbackLocaleOf,
   getFallbackOf,
-  getFallbacksOf,
-  setInitialLocale,
+  getRelatedLocalesOf,
   getCurrentLocale,
   $locale,
   isRelatedLocale,
 } from '../../src/client/stores/locale'
-import { get } from 'svelte/store'
+import { getFallbackLocale, configure } from '../../src/client/configs'
 
 beforeEach(() => {
-  setFallbackLocale(undefined)
+  configure({ fallbackLocale: undefined })
   $locale.set(undefined)
 })
 
 test('sets and gets the fallback locale', () => {
-  setFallbackLocale('en')
+  configure({ fallbackLocale: 'en' })
   expect(getFallbackLocale()).toBe('en')
 })
 
@@ -42,31 +41,35 @@ test('gets the next fallback locale of a locale', () => {
 })
 
 test('gets the global fallback locale if set', () => {
-  setFallbackLocale('en')
+  configure({ fallbackLocale: 'en' })
   expect(getFallbackOf('it')).toBe('en')
 })
 
 test('should not get the global fallback as the fallback of itself', () => {
-  setFallbackLocale('en')
+  configure({ fallbackLocale: 'en' })
   expect(getFallbackOf('en')).toBe(null)
 })
 
 test('if global fallback locale has a fallback, it should return it', () => {
-  setFallbackLocale('en-US')
+  configure({ fallbackLocale: 'en-US' })
   expect(getFallbackOf('en-US')).toBe('en')
 })
 
 test('gets all fallback locales of a locale', () => {
-  expect(getFallbacksOf('en-US')).toEqual(['en', 'en-US'])
-  expect(getFallbacksOf('en-US')).toEqual(['en', 'en-US'])
-  expect(getFallbacksOf('az-Cyrl-AZ')).toEqual(['az', 'az-Cyrl', 'az-Cyrl-AZ'])
+  expect(getRelatedLocalesOf('en-US')).toEqual(['en', 'en-US'])
+  expect(getRelatedLocalesOf('en-US')).toEqual(['en', 'en-US'])
+  expect(getRelatedLocalesOf('az-Cyrl-AZ')).toEqual([
+    'az',
+    'az-Cyrl',
+    'az-Cyrl-AZ',
+  ])
 })
 
 test('gets all fallback locales of a locale including the global fallback locale', () => {
-  setFallbackLocale('pt')
-  expect(getFallbacksOf('en-US')).toEqual(['en', 'en-US', 'pt'])
-  expect(getFallbacksOf('en-US')).toEqual(['en', 'en-US', 'pt'])
-  expect(getFallbacksOf('az-Cyrl-AZ')).toEqual([
+  configure({ fallbackLocale: 'pt' })
+  expect(getRelatedLocalesOf('en-US')).toEqual(['en', 'en-US', 'pt'])
+  expect(getRelatedLocalesOf('en-US')).toEqual(['en', 'en-US', 'pt'])
+  expect(getRelatedLocalesOf('az-Cyrl-AZ')).toEqual([
     'az',
     'az-Cyrl',
     'az-Cyrl-AZ',
@@ -74,10 +77,10 @@ test('gets all fallback locales of a locale including the global fallback locale
   ])
 })
 test('gets all fallback locales of a locale including the global fallback locale and its fallbacks', () => {
-  setFallbackLocale('pt-BR')
-  expect(getFallbacksOf('en-US')).toEqual(['en', 'en-US', 'pt', 'pt-BR'])
-  expect(getFallbacksOf('en-US')).toEqual(['en', 'en-US', 'pt', 'pt-BR'])
-  expect(getFallbacksOf('az-Cyrl-AZ')).toEqual([
+  configure({ fallbackLocale: 'pt-BR' })
+  expect(getRelatedLocalesOf('en-US')).toEqual(['en', 'en-US', 'pt', 'pt-BR'])
+  expect(getRelatedLocalesOf('en-US')).toEqual(['en', 'en-US', 'pt', 'pt-BR'])
+  expect(getRelatedLocalesOf('az-Cyrl-AZ')).toEqual([
     'az',
     'az-Cyrl',
     'az-Cyrl-AZ',
@@ -87,9 +90,9 @@ test('gets all fallback locales of a locale including the global fallback locale
 })
 
 test("don't list fallback locale twice", () => {
-  setFallbackLocale('pt-BR')
-  expect(getFallbacksOf('pt-BR')).toEqual(['pt', 'pt-BR'])
-  expect(getFallbacksOf('pt')).toEqual(['pt'])
+  configure({ fallbackLocale: 'pt-BR' })
+  expect(getRelatedLocalesOf('pt-BR')).toEqual(['pt', 'pt-BR'])
+  expect(getRelatedLocalesOf('pt')).toEqual(['pt'])
 })
 
 test('gets the current locale', () => {
@@ -98,10 +101,19 @@ test('gets the current locale', () => {
   expect(getCurrentLocale()).toBe('es-ES')
 })
 
-test('sets the global fallback when defining initial locale', () => {
-  setInitialLocale({
-    fallback: 'pt',
-  })
+test('if no initial locale is set, set the locale to the fallback', () => {
+  configure({ fallbackLocale: 'pt' })
   expect(get($locale)).toBe('pt')
   expect(getFallbackLocale()).toBe('pt')
 })
+
+test('if no initial locale was found, set to the fallback locale', () => {
+  configure({
+    fallbackLocale: 'en',
+    initialLocale: {
+      hash: 'lang',
+    },
+  })
+  expect(get($locale)).toBe('en')
+  expect(getFallbackLocale()).toBe('en')
+})