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From the HN comments:

That's a good point. Latin letters map to a big number of IPA sounds. I think this is specially true with consonants. Vowels, however, might be the same. For example, Spanish has five vowels (a, e, i, o, u in IPA). Japanese also has five IPA vowels and only the "u" is different in IPA

That's even truer for vowels than for consonants. Consonants are somewhat discrete, as they tend to gravitate towards certain articulations; vowels however are mainly defined by height and backness, and both features form a huge and messy 2D continuum.

With that said, the similarity between Spanish and Japanese isn't quite a coincidence. It's just that your typical language has:

• 2 to 4 vowel heights; often three (open, mid, closed)
• two degrees of backness, front vs. back
• less open than closed vowels

Once you glue those things together you end with a five vowels system, similar to Spanish or half Japanese. (Why half? Japanese distinguishes between long and short vowels, Spanish doesn't.)