While there is no absolute true and false when it comes to pronouncing foreign names and words in English,* I would like to discuss the pronunciation of Porsche, which has puzzled me and many others for quite a while. Whereas some companies choose to use a very different pronunciation of their name in other countries (good examples are Michelin, Wilkinson in Germany), Porsche uses an English pronunciation that closely follows the German one. A good example is this video from 2014:
Hence, Porsche is roughly pronounced as [pɔːrʃe], corresponding to the por- in “porch” plus the che- in “chef”. Because the speaker in the commercial has an American accent, the r is pronounced. The corresponding British pronunciation would be [pɔːʃe]. Note that the e sound for the letter e in [pɔː(r)ʃe] is an approximation, as discussed below. In principle, this is all you need to know if you want to use the original pronunciation. However, the story does not end here, and there are some interesting twists to come.
According to the Longman Pronunciation Dictionary, we have
[pɔːʃ] or [pɔːʃə]
in British English, and
[pɔːrʃ], [pɔːrʃə], or [pɔːrʃi]
in American English. The first variant, [pɔː(r)ʃ] is reported as being the most commonly used. Hence, in contrast to the pronunciation I gave above, [pɔː(r)ʃe], Longman suggests that the letter e is not pronounced at all. This makes sense, because a final e is usually not pronounced in English (examples include give, make, stage, or the originally French words niche and moustache). Alternatively, if it is pronounced, is sounds either like [ə] or as [i]. The schwa sound [ə] is the same as at the end of comma, whereas [i] appears at the end of me. Hence, none of the three variants given in the dictionary (and widely used in spoken English) matches the pronunciation used in the Porsche commercial!
Interestingly, you will often hear and read that the second variant, [pɔː(r)ʃə] is the correct pronunciation because it matches the German pronunciation. If you know the TV show Friends, you may remember the episode where Joey insists on the (wrong) pronunciation, see here for the transcript. However, [pɔː(r)ʃə] is simply wrong. By German standards, [pɔː(r)ʃ] would be correct if the name was spelled Porsch, [pɔː(r)ʃə] would be correct if it was spelled Porscha or Porscher, and [pɔː(r)ʃi] would be correct if the spelling was Porschi. Other people claim (for example, here) that Porsche is pronounced as Porsch-uh or Por-shuh (the simple but ambiguous way of avoiding to write [pɔː(r)ʃə]) . However, uh is pronounced either as [ʌ] or [ɜː] (see here), so that is certainly not correct.
Ironically, even phonetic spelling does not completely solve the problem (the phonetic alphabet was invented to give each sound a unique symbol). The Longman Pronunciation Dictionary also includes the German pronunciation [pɔːʁʃə], which should be compared to the pronunciation given by the Duden, [pɔːrʃə]. First, note the different symbols used for the r (Longman uses ʁ to distinguish it from the English r, whereas the Duden uses r for the German r because it is a German dictionary). More importantly, the schwa sound [ə] is not the same sound in English and German. In English, the schwa appears at the end of words such as comma. In German, there are two schwa sounds (schwas are so-called reduced vowels). The [ə] schwa (also called e-Schwa) appears in words such as halte or lese (with German phonetic spelling [haltə] and [lesə], respectively). It is therefore not identical to the schwa in English words such as metre or silver, but instead sounds much more like the [e] in chef or test. On the other hand, there is also a German schwa sound that is identical to the English schwa (the a-Schwa or Lehrerschwa, so called because it is exactly how –er at the end of Lehrer is pronounced). The latter is denoted in the Duden as ɐ. With this insight, the pronunciation of Porsche can be understood by comparing the German words
Lehre (German phonetic spelling [le:rə], listen here)
Lehrer (German phonetic spelling [le:rɐ], listen here)
Lehre ends in an e-schwa exactly like Porsche, whereas Lehrer ends in an a-schwa. However, because Porsche ends in e rather than er, the correct sound is the e-schwa. Whereas [ə] and [ɐ] sound very different to the ears of German native speakers, they may sound quite similar to English native speakers. Even wikipedia incorrectly claims that the two sounds are identical, see here. John Wells (author of the Longman Pronunciation Dictionary) confirmed to me that English speakers typically have a hard time distinguishing the two German schwa sounds, and therefore replace the e-schwa by the a-schwa. Another example discussed on his blog is Miele. Hence, Por-shuh is indeed a common English pronunciation of Porsche (as suggested by the dictionary), but it does not match the original German pronunciation.
Conclusion: The correct pronunciation of Porsche is a hotly debated topic. As a native German speaker, I can assure you that Porsche is never pronounced Por-shuh in German, simply based on the rules of the German language. In fact, the poor man’s phonetic spelling Por-shuh is wrong even in English, because uh is pronounced either as [ʌ] or [ɜː] but not as [ə], see here. (There is a good reason for using real phonetic spelling.) Therefore, I suggest to stick to the most common English pronunciation, [pɔː(r)ʃ], or to make the effort to get the letter e right if you are aiming for the original pronunciation used by Porsche. So, strictly speaking,
PS: If anyone from Porsche is reading this, I have always wondered exactly how much fun it is to drive a Porsche …
* The motivation for changing the pronunciation is that foreign words often contain sounds that are not part of the English language (e. g., umlauts). Such sounds are often approximated by the most similar English sounds. This approach is typically used when using words from less widely used languages in very common languages such as English. However, because of the wide-spread use of English, English words are often pronounced with non-German sounds (most notably the th) even in German, see here.