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> Any idea if this is why, in Japanese-dubbed anime, the voice actors seriously mangle some English words/names? E.g., they often add a vowel sound to the ends of English words that should end with a percussive syllable.

I don't know anything about anime, and little about Japanese, but I think Japanese (and Chinese) have a fairly strict consonant-vowel form for all their syllables. That makes foreign words that have runs of consonants or do not end it a vowel hard to pronounce, so speakers of those languages have a tendency to insert extra vowels to make pronunciation easier for themselves.

It's kind of like how English speakers will usually change the Pinyin "X" (as in Xi Jinping) into an English S or SH sound when they try to speak it, because the actual sound doesn't exist in English.