The Bug:
You cannot double-click on languages within the "Language" menu to select them.
Within similar menus such as the singleplayer world list and the multiplayer server list, you are able to double-click on fields within the list to interact with them, but this is not the case with fields in the "Language" menu, therefore introducing a slight inconsistency. This may possibly be considered a feature request but it's quite a handy mechanic as it's generally convenient for players.
Steps to Reproduce:
Navigate to the "Language" menu.
Double-click on any language within the list in an attempt to change your game's language to that language.
Take note as to whether or not you can double-click on languages within the "Language" menu to select them.
Observed Behavior:
You cannot double-click on languages to select them.
Expected Behavior:
You would be able to double-click on languages to select them, just like how you're able to double-click on fields within the singleplayer, multiplayer, and realms menus to interact with them.
I can confirm this behavior.