Although Master’s and Bachelor’s degrees have now spread far beyond English-speaking countries, there is still a lot of confusions about the correct spelling. Importantly, in expression such as
Master’s thesis, Bachelor’s thesis, Master’s degree or Master’s student,
the apostrophe is part of the correct spelling, indicating that the thesis was written by a person that is now a Master or a Bachelor. (Interestingly, the expression Doctor’s thesis is not common among native speakers, instead the terms Doctoral or PhD thesis are used). Anyway, if you are the proud owner of Master’s or Bachelor’s degree, make sure you spell it correctly in your CV etc. The same applies if you are advertising a position for a Master’s student in English, or typesetting the front page of your thesis written in English.
A google search for Bachelor and Master thesis seems to imply that incorrect spellings (leaving out the apostrophe and the trailing s) are almost always found on (English-version) websites of non-native universities and people, whereas they are almost always included in the case of English-speaking institutions and persons.
Finally, many languages have their own version of the above English expressions. For example, in German, the words Masterarbeit and Bachelorarbeit, and the mixed-language expressions Masterthesis and Bachelorthesis (see here for their pronunciation) exist. However, those are supposed to be used in German only. For example, I have recently come across the term Master work here in an English document here Germany.