If a user copies someone else's article or a post from the forum, then translates it into another language, and posts a new post in the locale into which the text was translated.
Is this considered plagiarism, with the condition that there are absolutely no links to sources? That is, we can assume that the person who wrote the post assumes the authorship.
It can be taken as a translation, but I think the user needs to make it clear in the topic title that this is a translation. They can include the source if they want but as long as it says translation they should be fine.
However, if this is a translation using any automatic translation software then there are things to be concerned. And these days users also your article spinning software too. If the translated lines and formation of the words are following a specific pattern then this will surely be an article spinning using automatic software.