This is currently the most complete localization system available for Unity.
Unity UI, Unity 2D, TextMesh Pro, NGUI, 2D ToolKit, SVG Importer, Standard Components
Image, Text, Sounds, Fonts, Sprites, Atlases, Prefabs, TextMeshes, Dropdowns and more.
Built-in support for Google Translator to automatically localize all your labels into any language.
Google Spreadsheets and CSV files
Link external Spreadsheets and any change will be automatically downloaded, even after the game is released.
Detect and Fix Errors
Parse scenes to find missing or unused translations as well as duplicated or similar terms.
Set Secondary terms to change not just text and images, but also which Fonts and Atlases are used per language.
Callbacks and Parameters
Translations can be modified to insert Scores, Names and Game Variables using the languages grammar.
Built-in rules for each language covering those that just need singular/plural forms up to those that use 6 variants.
Right to Left Languages
Correct rendering of RTL languages with support for line wrapping and alignment.
Create Fonts with only the characters you are using. Link your AssetBundles to add more localized content.
Easy and Efficient
Edit and Preview all your translations in one location, then, at runtime only the current language is loaded. Using fast lookups to access it.
Set texts to be automatically shown as UPPER CASE, lower case, Upper first, Title Case, etc.
In Game Dynamic Translations
Easy API to translate chat messages and other dynamic texts at runtime
App Name and Store Localization
Translate the name of your game to all languages and show in the Android/IOS store which languages your game support
Simple yet Powerful Editors
Intuitive inspectors allow you Preview, Edit, Categorize, Create, Parse and Filter even large sources.
Compile Time Checking
Bake translations into script constants to avoid Typos when accessing them on the code.
Several actions to access and interact with Localized elements and switching languages
More Info: _https://assetstore.unity.com/packages/tools/localization/i2-localization-14884