The language which translate the post is NOT up to the SFDC lanaguage settings of the user who posted, but the language settings of other user who can see the post.
For example, when a user A posted “Today’s weather in Shanghai is sunny” to his own feed (timeline) ,
if there are User B (SFDC language setting=Japanese) and User C (SFDC language setting=Chinese(Simplified)) following user A,
the language settings of other user who can see the post would be Japanese and Chinese(Simplified)
Therefore,
- 「上海の今日の天気は晴れです。」(Japanese)
- 「今天的上海天气晴朗。」（Chinese (Simplified)）
will be the translation output as the result. No matter what the language settings of user A is.
You can take the language settings of other user who can see the post into account as
- The user language of the follower and the followee of the user who posted （Timeline (user feed) translation）
- The user language of the user mentioned (Mention translation)
- The user language of the group member in the group which the user posted to (Group translation)
- The language of the user who follow the object, when the post was to an object feed.(Object feed translator)
- No matter what kind of support license of the user who can see the post. (Please note that the poster must be a user in supported license)
For further information, please refer the supportive article “Description of functions”