In 16w32a, there was a bug (MC-105948) which didn't let you change language. In 16w32b, the pre-selected language is English (US)… even if you have an another language already selected.
For example, I'm French and play with Français (France)… but the pre-selected language is English (US), even if I have french texts.

You can see this in the second attachment, where "English (US)" is selected… with french texts.

steps to reproduce:

1. start 1.10.2 in non-en_US language
2. stop
3. start 16w32b

Note:
Selecting the selected language fixes it.