This isn't strictly true. The Android version was designed so that we could switch to another mapping provider if we decided to, and on iOS we use Apple Maps as the mapping provider, not OSM. Much of the language is shared between different providers because a lot of it derives from earlier standards such as WGS84, which predates all of the web-based map providers.
MIT doesn't provide translations. Translations are created by volunteers who think it is worthwhile to have App Inventor translated into their native language. Often, it's a group of teachers or people running a coding camp who think it would be helpful for their young students to have the interface in both languages so they can learn the associations between the technical terms in their native tongue and the English equivalents.
We attempt to verify translations using machine translation techniques but that doesn't really beat native speakers reviewing the changes. For example, in the Turkish translation the word "tan" for the math block "tangent" was translated as the color tan. Only after a native speaker saw it in context was the flag raised but we don't get that context from machine translation
App Inventor does have a mechanism to present different translations of the reference documentation based on the locale the user specifies in editor. However, while this is deployed we don't have any translations for it yet, partly because this isn't well advertised and partly because there is a lot of documentation to be translated so it is a fairly daunting task.