@astefanowitsch Sorry, forget the question, I wasn't thinking.
A→C does obviously not follow from A→B and B→C, because B could be a homonym while A and C are not (at least if we only demand A and B to have the same meaning, and B and C, but B may have different meanings in A→B vs. B→C).
Example: consider the English word "Jaw".
"Jaw" (English) → "Kiefer" (German)" → "Pino" (Spanish).
But "Jaw" (English) is not "Pino" (Spanish), because "Kiefer" (German) is a homonym. And this doesn't even involve cases where a concept exists in only one language.
On the other hand, if we do demand the same meaning for B in both cases the whold thing is trivial.