Is it possible to write the abstract in more than 2 languages

Whether it's 'allowed' or not, formally speaking, is exclusively the decision of your institution. However, this is your thesis, and within reasonable parameters you can and should do with it what you feel is right. Adding an abstract in your own language is certainly well within the field of reasonable.

In particular, it's important to note that many universities in Germany actually force you to write an abstract in German even if the thesis is in English (example), so adding an abstract in German is simply part of a standard practice in the country. Adding an abstract in a third language, which only adds value to the thesis without subtracting anything, is not that far from that.

That said, to be safe, you should still check with your institution - the library, or the director of postgraduate studies, or whoever is in charge of thesis submissions - that this is OK. If they say no, then you can still try to negotiate your way around it (leveraging your supervisor and other staff if necessary), but it's unlikely that they'll refuse.

It all depends on your institution. I did my PhD in Barcelona and while the PhD program was in English, the University insisted on an abstract in Catalan. The result was two abstracts, one in each language.

Furthermore, I chose to write the Acknowledgements section in a mixture of English, Greek and Spanish, depending on whom I was thanking, bringing the total number of languages used in the thesis to 4 (or even 5 if you count a couple of phrases in French).

In other words, yes, it is indeed possible, at least in some universities, to mix languages in your thesis. I doubt any would allow you to do so in the main body of the document, but both the Abstract and the Acknowledgements should be fair game. Nevertheless, the only people who can answer this for you are the relevant employees of your university.