Date her or him for 20 years first then tie the knot.
No point rushing these things.

And learning the language will always help.

Now come on chaps.......Fun forum yes, BUT I want to help with stuff.......If I/we can...Sort of my baby..

I've been at this Thai stuff nearly 30 years (28 to be precise) I found words in our language that have helped me during good times and bad - I used them all the time "sure" it gets me out of tinking too mutt and they feel in control which is much much easier than debating. The other is "interesting" when I use it it can mean anything from I'm bored to I don't give a flying fcuk.

I also figured out the "up to you" many moons ago, never ever give options I would ask as an example "would you like KFC or McDonald's for lunch and the reply was "up to you"' when giving options and you hear "up to you", it's a test, a game of sorts and I would suggest run and hide - by giving suggestions and them using "up to you" they are allowing you to think you are in control....... It's the opposite they already know they want KFC and dammit you better pick the right one.

What we forget is that we aren't just hooking up with a soul mate, we are marrying a family, the deaf old Auntie who craps her pants and who's locked in the shed probably has more say and control over out relationship than we realise. Sad as that may sound I wouldn't have changed a thing just bought her better adult nappies.

Some Thais don't travel well, mine ended up hating Thailand and I was the one keen on living here, I'd do it all over again in a heart beat. Show them the world and break them in to thinking outside the border, if you can't do that learn the words "sure" and "interesting"

Learn Thai time, which when a Thai dpeaks in English, is normally expressed as "soon, not long, later or after food" all of which are interchangable,and bear no relationship to hours, minutes or seconds.

Sorry that will not work.
Leangth  of knowing them does not matter much.  what matters is how you get on and how secure you are.
Thais need security and often problems start with a change in finances.  It is not really the money, it is not knowing how they will survive.  You can know them for 20 years, marry them and break up the next week. You can live with someone for tweenty two years, your security ends and problems start or you can live with them forever.
It is important to recognise the need.

Of course language is needed. If you are not prepared to learn it you cannot expect to live happily.

So she doess not call you sonnney or babeeeee.
I do not think you need to be fluent....or have a huge vocabulary, but have at least a willingness.

It drives me bonkers, have you ever noticed it's the same guys when walking with their wives and see another farang within ear shot, start speaking in English rather loudly as if to say hey look my honey can understand English. All the time I'm thinking I'd be more impressed if I heard you speaking Thai.