Is it tex(tech)? Or Is it tex(like touch)?
Lay-TeX? or La-TeX?
Should I use TeX pronunciation in LaTeX?
Let the creators of TeX and LaTeX answer:
Donald Knuth wrote in the first chapter of his TeXbook:
English words like ‘technology’ stem from a Greek root beginning with the letters τεχ...; and this same Greek word means art as well as technology. Hence the name TeX, which is an uppercase form of τεχ.
Insiders pronounce the χ of TeX as a Greek chi, not as an ‘x’, so that TeX rhymes with the word blecchhh. It’s the ‘ch’ sound in Scottish words like loch or German words like ach; it’s a Spanish ‘j’ and a Russian ‘kh’. When you say it correctly to your computer, the terminal may become slightly moist.
Leslie Lamport wrote in the first chapter of his book LaTeX: A document Preparation System:
One of the hardest things about LaTeX is deciding how to pronounce it.This is also one of the few things I'm not going to tell you about LaTeX, since pronunciation is best determined by usage, not fiat. TeX is usually pronounced teck, making lah-teck, and lay-teck the logical choices; but language is not always logical, so lay-tecks is also possible.
Using the IPA, it is /ˈleɪtɛk/, /ˈleɪtɛx/, /ˈlɑːtɛx/, or /ˈlɑːtɛk/.
LaTeX is usually pronounced /ˈlɑːtɛk/ or /ˈleɪtɛk/ in English (that is, not with the /ks/ pronunciation English speakers normally associate with X, but with a /k/). The characters T, E, X in the name come from capital Greek letters tau, epsilon, and chi, as the name of TeX derives from the Greek: τέχνη (skill, art, technique); for this reason, TeX's creator Donald Knuth promotes a pronunciation of /ˈtɛx/ (tekh) (that is, with a voiceless velar fricative as in Modern Greek, similar to the last sound of the German word "Bach", the Spanish "j" sound, or as ch in loch). Lamport, on the other hand, has said he does not favor or discourage any pronunciation for LaTeX.
I think that it's better to find out what Knuth has to say in the matter... Listen!!! :D
Oh, and watch the whole presentation. It is definitely worth it.
Knuth answers this in the TeXbook: it's "teccch" (a gutteral sound, like in German or Russian or Hebrew, or of course Greek) not "teks" or "tetch". According to the TeX FAQ, there is no official pronunciation for LaTeX, but I often hear "lay-TeX" or (of course) "lay-teks" for humorous reasons. I prefer "lah-TeX", as in "Lamport", but I'm pedantic.
TeX actually stands for tau-epsilon-chi and the 'X' is therefore pronounced like the 'ch' in German, i.e. by breathing out through half closed mouth (I can't explain it better). It's sounds similar to the 'tech' in 'technique'.
The TeX Wikipedia page says:
TeX (/ˈtɛx/ as in Greek, but often pronounced /tɛk/ in English) ... 'ch' like in 'loch'
LaTeX is pronounced lah-tech by most German speakers (like me) but in English it is often pronounced lay-tech. IMHO that is because it is the natural pronounced of that languages.
Allow me to suggest a probably unpopular alternative: "latex" /ˈleɪtɛks/. Like the substance. Let it stand for whatever Greek letters it may: I'm not reading it in Greek, so that's irrelevant. Spell it like an existing word and you only invite a reader to read it like an existing word.
Ultimately, I'd posit that it's not that important as long as people understand you.
(Also, SQL is not "sequel" and "arXiv" is not "ar-kh-iv" (and definitely not "archive").)
Here, in the answer to the third question, Leslie Lamport pronounces TeX and LaTeX as
lay-tek respectively, although @gonazalo-medina mentioned a very good reference and I also personally prefer