Looking at the list of academic ranks on Wikipedia shows that the same academic rank/title can mean quite different things in different countries. For instant, a "research assistant" in the US can stand for an undergrad student doing an internship, while in the UK it can stand for a postdoc. Similarly, the term "lecturer" might stand for a permanent position (e.g. in the UK) or for a teaching assistant position, open to graduate students.
However, when thinking about it, there are not so many kind of possible positions (permanent or not, with teaching or not, with research or not, with PhD supervision or not, with team responsibility or not, etc), and having a clear title could help a lot (for instance, in my case, I've been working in four different countries, with a different job title each time!).
- Is there some kind of official taxonomy that one could refer to?
- If not, who could be in charge to create it? (the EU, if only for intra-Europe mobility?)
In general, the answer is negative.
Not only there are different systems in different countries (and same-spelled degrees may have different requirements), but even if a degree seems to be the same, it is not necessary considered equivalent.
Often universities and institutes have some freedom in the interpretation of degrees earned in other countries. Common sense can be a good guide but in case of doubt you need to check if university (or institute) X accepts a foreign academic title Y instead of their Z.
For example, when I obtained degrees licencjat (3 years undergraduate, 180ECTS) and magister (5 years undergraduate, 300ECTS) from a Polish university, they refused to translate it into anything else (stating explicitly that it is not equivalent to anything else). However, some other Polish universities do translate it into Bachelor of Science and Master of Science, respectively. Nevertheless, my new institute didn't have problem to find them qualifying me for their PhD program.