Spanish also has that property, i.e. given a word (existing or invented), there is a single way to pronounce it, easy to determine following some rules.*

Finnish (from what I've heard, as I don't speak it) is even more regular in the sense that this also works the other way around, i.e., if you hear a word, you can use rules to know how to spell it. This does not always hold in Spanish (e.g. B and V are pronounced the same, so you cannot know if you're hearing "vaca" or "baca" without resorting to context and common sense reasoning) although it does hold for all but a small bunch of grapheme pairs.

* Modulo regional variants, but if you focus in any given variant (e.g. Spanish from Spain) this holds.

Finnish is not unique in that it has quite a few dialects like most other languages.

> And the least phonetically consistent is English.

I guess maybe they're not "languages you know", so your statement is still accurate, but surely the Chinese languages and Japanese are even further than English on this spectrum. Some (but not all) Chinese characters encode how the character was pronounced in ancient Chinese, which might give a vague hint to how it's pronounced in modern Chinese languages, but that's about it. And Japanese is even worse: most Japanese words are written using Chinese characters, but the same character can have several different pronunciations (for example, the same character might have three pronunciations: one for a Chinese loanword, another for the same Chinese loanword that entered Japan in a different century, and a third for a native Japanese word whose pronunciation isn't connected to the Chinese pronunciation at all). Also, one character in Japanese can have a several syllable pronunciation, whereas in Mandarin and Cantonese at least, polysyllabic characters are extremely rare.