Hi everyone!

I am new here, haven't started learning Thai yet, but looking to do so soon.

A little bit about my background in languages. I have been speaking Vietnamese and English since I was a child. I also speak intermediate level Japanese and understand some Chinese.

Is there anyone out there who speak Vietnamese and have use that knowledge to learn Thai? I would assume it is easier to learn Thai using Vietnamese versus using English. Also does anyone know a good Vietnamese - Thai dictionary (not book)?

Speaking Vietnamese will give you a head start. In particular, the ability to produce the tones - though the Thai tone system is rather different from (but simper than) the Vietnamese one.

I think you'll find it difficult to get Thai/Vietnamese resources - Thai/English ones are much more common.

As for learning Thai with English versus Vietnamese, most textbooks and courses use one of two systems to represent Thai using Roman letters plus a scattering of IPA characters and tone marks. Both systems are very easy to pick up. There do exist similar systems in other languages such as Japanese. There's probably a similar system using the Vietnamese alphabet (I don't know). However, it wouldn't have any inherent advantage over the Roman alphabet-based one. I have studied Thai with Japanese, Chinese. Korean and Russian students - many of whom spoke little or no English - and none of them had a problem with the Thai language representation.

So, putting aside the system of writing Thai, it really comes down to a matter of lexis: would you find it easier to understand a Thai word from an English explanation or a Vietnamese one?

Given your apparent ability in the English language and the scarcity of Vietnamese-language resources I would think that learning in English would be the better for you.

Good luck with your studies!

In an addition to AyG's excellent answer.

Teach yourself not to be confused with Thai transcription, especially IPA tone marks as they are very different to those used in both standard Vietnamese and 拼音 (pinyin).

And good luck!

I believe the overwhelming issue here is resources, which makes English the better choice. As for romanization or transliteration - there are many, many systems (not just 2). Wean yourself off of it asap to avoid confusion.