CrowdIn allows unlimited users to add content to a localization. Any user from any website can improve a language pack. Even just one phrase if they want. This means that language packs are under continuous development by a very high number of users. Large forums like reddit use it with good reason. Reddit lists their translations as one of their main achievements.Which is not surprising considering that translations are the requisite for making a website available in multiple countries and reach critical mass.
Crowdin | Localization Management Platform
Modern Localization Management: Collaborative nationalization and easy to use translation service tool: collaborative nationalization and quality translation platform Crowdin
reddit translations: collaborative nationalization and quality translation tool Crowdin