Keep me posted/updated ？
is this mean "Let me know the latest/most recent news "?

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This can be mean to let you know the latest information

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ｏr to　“ｋｅｅｐ　ｍｅ　ｉｎ　ｔｈｅ　ｌｏｏｐ＂，　ｂｕｔ　Ｉ guess that's another variation that's hard to interpret. 
It just means that if something new happens, please keep me informed.  For example, if you are involved in a project, then you may want to always know what's going on.    
It's not really the same as "let me know the latest/most recent news", because it has a cyclic meaning and the news is not assumed to just occur once.  For example, "If you have any new news, please let me know" can be used to substitute.

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plz write me lahcen2100arobaslive.fr

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Does this mean....

Yes it does.