[robocat]

In English we are really familiar with wildly varying vowel sounds.

Is French similar to Spanish? A change in vowel often completely changes the word and makes it incomprehensible.

Aside: if your mother tongue is English and you want to speak to a person whose native tongue is Spanish, concentrate very hard on the correct vowel sounds when speaking Spanish. Vowel fluidity is ingrained into English (especially between dialects), but vowel constancy is ingrained into Spanish (even across countries). If you are speaking English words to a Spanish listener, you can help them by speaking the words with transliterated Spanish vowel sounds from the written words. This is especially useful for the names of celebrities or place names e.g. Michael Jackson is said differently in Spanish. Also Sir Francis Drake is literally Pirate Drake in Spanish.