Caterham is "Cater-rum", with the latter syllable's vowel sound varying depending on regional accent.
It's sort of lazy really, but that's how it's become. The same applies for practically any place name ending in -ham in the UK, e.g. Birmingham.
It's definitely not "Cater-ham", nor "Catter-ham" or any other kind of ham.
EDIT: Beaten; that'll teach me not to post immediately.
The reason Germans "struggle" with squirrel is because "qu" is always "kv" in German: e.g. "
quatsch" ("Kvatch"). They don't really do
ws, and the leading
s in squirrel probably really messes things up. The double
r is a red herring, its behaviour is more consistent in German (less French and Brythonic / general Celtic influence), but the effect of the double
r in squirrel is analogous to how it would work in German.
EDIT:
Squirrel appears to be some sort of litmus test for pronunciation, Google translate struggles with it too!
According to Google Translate, Nissan is pronounced differently than all of you guys have said. Not knee-san or niss-ann, more like a combo of the two. It's supposed to be knee-sann or niece-ann or neese-ann, but with no break between the s and the a. So knee-san but the a is short, as in apple.
It's the same vowel sound as "knee", but in "Nissan" it's a short vowel not a long one as it is in "knee", which is why the latin / romaji transliteration has a double
s, which also shifts the syllabic stress onto "san" -
compare. The length of the vowel is equally important as the vowel itself, and intonation and stress just the same.