Match app UI language to system language on first run

[bitigchi]

Lagrange should get the system language string and set the UI language automatically at first start.

[skyjake]

This would be a nice little improvement to the first-use experience. On Unix systems at least there's the LC_* environment variables that could be checked.

However, the cost/benefit ratio isn't super great. Determining the system language is platform-specific, and doing this only on one or two platforms limits who will receive the benefits even further, in addition to being limited to new users.

That's not to say it's not worth doing, but it may not make practical sense at the moment.