Could it also be: he works already seven years here? "děla" is present and "už" should also be translated somehow. Or: he has been working here already seven years
We would understand, but the way you shuffled it sounds wrong in normal conversations. If I look at it from a different perspective, it also sounds poetic.
Since Czech has only one present tense, it has to do the work of multiple present tenses that exist in English. Here, the action began in the past and is continuing, so we need "has worked" or "has been working."
Translations that use "already" are accepted.
But The placement of "already" is your suggested sentence ("already seven years") is incorrect. Accepted translations that are similar to your second one are "He has already been working here seven years" and "He has been working here seven years already.."
I also do not understand what UŽ contributes here. One might get a better understanding of this issue if we had a translation of the Czech sentence without the UŽ in it. Does it sound strange without UŽ, or conveys a different meaning?
The meaning is almost the same, it can just emphasize that the speaker thinks that it is a long time or a time sufficient for something.
Please understand that first the Czech sentence is created and only then the English one as its translation. The Czech sentence/answer here was not created as a translation of this English sentence.
"He has already worked here fo seven years" I think the meaning is the same but it is not accepted.
"He has already worked here FOR seven years" is indeed accepted. If that was exactly what you wrote, you may have run into the grading bug that pops up now and then. (If not, the word "for" is just misspelled in your comment.) We suggest using the Report button, so that the team can see your actual translation and, if it's wrong, tell you why.