Short version:
This release of on-demand channels post translation will allow you to translate channel posts that are in another language, into the language of your choice. This is rolling out in the Teams iOS and Android stores early June to mid-July.

Details:
This release of on-demand channels post translation will allow you to translate channel posts that are in another language, into the language of your choice. This is rolling out in the Teams iOS and Android stores.

To translate, press and hold the message and then tap Translate. To return a translated message to the original language, press and hold the message and then tap See original (language).



To set the language that you want messages translated to, tap Settings Translation and then choose desired language:

Admin stuff:
The ability to translate messages will be on by default. To disable, follow these steps mentioned here.

Availability:
Microsoft will begin rolling this out in early June and expect to complete the rollout mid-July.