Marriage visa: if something tragic happens to your wife (sickness, motor bike accident) you have 72 hours to leave Thailand, leaving the children (if you have them) behing and come back on another visa.
If you really have strong dedication and attend the classess and do homework (rarely anyone on that visa does that, they hardly show up at the school) you might attain the profficiency to talk to street vendors, nothing serious.
6 months visa is all they need.
Upon renewal, Immigration officers talk to you in Thai only and quickly realize that.
Daughter speaks, reads, writes Japanese as grade 6. To get Thai to that level, for an adult, it may take years and years, even with dedicated full time courses as foreign goverments send their staff to learn Thai, 6 days x 8 hours a day for a year.
My daughter (21), a Thai national, her first language was Thai, left Thai as 4.5 years old. A student now in Australia. Raised in Japan, International School, English spoken at home.
She took so far 400 lessons from a professional Thai teacher (15 US$ an hour, online), reading, writing, speaking.
She can barely make a phone call from overseas to Thai.
I was single, with a "Non Impediment" from Australia. The officai marriage Sathorn, Bangkok, City Council , took 15 minutes and the official deed produced and handed over to us. Accepted everywhere.