[supergarfield]

This might be somewhat subjective, as I don't know how you'd measure correlation between spoken and written, but French seems to have a much higher match between written and spoken language than English.

Going from spelling to pronunciation in French follows (admittedly complex) rules that are rarely broken except for common words (or endings such as -ent). Vowel pronunciations for a given spelling are far more variable in English, and often depend on the etymology of the word. Plus, English has word-level stress that is not marked in writing (French has none, and it's marked in Spanish), and moving the stress will usually make a word unintelligible! That alone makes writing => pronunciation very difficult.

[gecko]

French spelling is unidirectional. I can comfortably say any French word (albeit with a couple key exceptions, such as "et" or "clef", that break rules), but I can't reliably go from someone talking to how to spell it. "Eaux", "eau", "au", and "aux", or alternatively e.g. "ou", "oux", etc., all have identical pronunciations, but different spellings.

Unsurprisingly, we can vaguely quantify this by looking at dyslexia amongst languages. English and various Southeast Asian languages that rely on Chinese ideographs are by far the worst, followed by things like Arabic, French, Hebrew, and German that have fewer exceptions but less guidance, and then followed last by things like Spanish, Cherokee, and so on that are truly one-to-one.

[eindiran]

> how you'd measure correlation between spoken and written

There are a number of ways currently used, but I have a new one to propose: compare the size of two G2P models (1 for each language), which have similar RMS errors. Assuming they are generated using similar techniques, the one which requires the bigger model probably has a less clean phoneme-to-grapheme correspondence.

[jgwil2]

It's not subjective; French is better than English in this regard, and Spanish is better than French. English has more complex pronunciation rules and many, many more exceptions than those languages.