Let me share some of the most interesting English blunders I encountered during a recent physics conference in Germany.
Mistake 1: Several German native speakers made the mistake of pronouncing the th in thermal and thermodynamic as a t rather than a θ. Since most of them pronounced other occurrences of th correctly, I suspect that they were confusing the English and German pronunciations of these words. You can hear the correct pronunciation of thermal here. For a general discussion of how to pronounce th, see here.
Mistake 2: I noticed that it is quite common for nonnative speakers to mispronounce the word engineering (as well as engineer). While the noun engine is stressed on the first syllable [‘endʒɪn], the stress in both engineer and engineering is on the last syllable (for example, [ˌendʒɪˈnɪə(r)]). Click to compare engine and engineer.
Mistake 3: In an effort to adopt an American accent, people sometimes make interesting mistakes, see here. A recent example is the pronunciation of because as [bɪkɔːrs] (corresponding to becourse) rather than as [bɪˈkɔːz]. While the letter r is pronounced very strongly in American English, there is no r in because. An even though a so-called intrusive r is sometimes added at the end of words, this is not common in the middle of words.