There was a joke among Thai language learners. It goes like this:
"If you learn Chinese, you get the grammar, but writing is a bitch.
When you learn Korean, you get the writing system, but you die by grammar.
When you learn Japanese, that's when writing and grammar are both hell for you."

turkish, and russian

@ mata I was under the impression you spoke a different language than thai, perhaps one specific to your ethnic group whatever that may be because of other posts you have made in the english topic.

Indonesian / Malay is still on my list... it's a pity I can't find any decent learning material.

Somewhat, but not all. People who know words from other dialects have easier time understanding it because all dialects are linked in some way. There're similar words used in two dialects, but not the other two, or this word is used in a dialect but not the other three (Tai-based languages in Thailand has 4 major Dialects. Each dialect is a language of its own.)

Also, how much does tone, and the meaning of words change between  dialects?

I have various dreams about learning various languages. It was for example Chinese, Japanese, Arabic ETC.
I know, that It is difficult to learn or write in Chinese, for example of writing chinese in computer is not very easy task, similar situation is sometimes with Japanese, but Korean uses Hangeul, Hanja (chinese characters) were used to write Korean.
I know, that Korean grammar is not very easy, but It is also good for update my brain. But I know, that for example, Malay, or Indonesian is easy to learn.

There are a number of languages I'd like to learn: Japanese, Danish, Welsh, German,and Russian to name a few. I'm very slowly in the process of learning Irish Gaelic, both for personal reasons, as well as for religious reasons.

I die when it comes to pronunciation in Gaelic, any form of Gaelic. There was someone trying to teach me that once and I got stuck. It's probably as amusing as when I taught a friend Thai and he died trying to get the tones right.
Tones are different in each Thai dialects. It changes acordding to meaning and expression. Different tone of the same word means differently, sometimes turning something good to something totally shitty. It's difficult to grasp especially among those who speak non-tonal languages. I seriously hate Thais who make fun of foreigners for mispronouncing words. It takes serious effort.
Words aren't the same in different dialects, because each dialect is actually its actual language, but subdialects within a dialect share similar words and stuff. It may be hard for Paktai or Isan speakers to grasp Lanna because they're different main dialects, different languages to be precise, but Lanna speakers of Lampang, Chiang Rai origins can speak finely with those of Chiang Mai and Lamphoon origins because both subdialects are Lanna, even though some words may be used differently. Example given is a word to call guava in these sub dialects. Lampang speakers call it "ma-mun" (pronounced Ma "m-un, as in unfortunate, mun" when Phrae speakers call it "ma-kuay-kaew" with "kaew" of highest rising tone. Chiang Mai speakers call it "ma-kuay-kaa". In this example, Phrae and Chiang mai spakers, though being one province apart (Lampang is between these two provinces), call guava similarly. Lampang speakers, being next to both, however, call it differently. Those using the same main dialect can tell where people they talk to are from by identifying tones and words used.

Actually a lot of the courses I’ve seen online teach you both formal and informal ways to say things, a Swahili course and a Spanish course, both actually on YouTube however the Swahili course had a website.  I can’t speak on any other courses.

Yeah, Irish is a tricky language to learn. It doesn't help me too much either that most of the places you learn it from tend to want to teach people the Ulster dialect when I specifically want to learn the Munster dialect.

Irish is the primary language I want to learn. I've been slowly learning it, word by word, over the past few years. Finally found an audio program that will help teach pronouncation a little bit better....Though it's hard to hear it properly at times. Especially when you speend it all the way up.

Like I said, there are multiple reasons for my wanting to learn irish. Religion is a large part of it. I practice a form of Irish folk religion, and knowing the language helps a lot. I specifically want to learn the Munster dialect because that's the dialect my grandfather spoke when he was still alive and some of what few words I know of it is in that dialect.

What is that? A word from  one of the 11 south african languages?