This is one of the biggest social barriers in Thailand, not only with Thai girls but with Thai people in general. This is because of the complexities of the English language itself, which often causes things to get lost in translation due to incorrect grammar and vocabulary.
When communicating with friends and acquaintances, it is usually not an issue and is easily correctable if communicating with friends, however in romantic relationships, daily misunderstandings due to language could snowball into bigger problems, so keep that in mind. To avoid potential language problems, it is recommended to speak slowly and using simple language to avoid any piling up of misunderstandings which could cause conflicts in the future.
Bear in mind that they are not in their comfort zone talking in English just as you are not comfortable talking in Thai, so be patient and take the time to explain when necessary.
The meaning and value of family are different between westerners and Thai people. Most Thai people, both men, and women are likely to still be living with their family even as an adult, even as a Thai woman marries, they still want to either live with their own family or the husband’s family. This might be something uncommon in the western world, but in Thailand, it's completely normal.
One thing to keep in mind when in a relationship with a Thai woman is that her allegiance will always be to her family for example when they need emotional or financial help, family always comes first. Sometimes this might change when you have children with your Thai partner as they will then always put their child first.
When deciding to get serious with a Thai woman, her allegiance to her family must be accepted even though it may be drastically different from what you're used to. Elders in the family, especially parents and grandparents, are to be respected unconditionally at all times.
Westerners with Thai girlfriends or wives usually mistakenly assume that a lot of their relationship is based on money, however, this is usually not the case. Granted that it might be to some extent, but not for the reason you would think. The face is a very important aspect of that society, which goes hand in hand with money.
Having money or seeming successful is very important in Thai culture, maintaining “face” is important for you to have a good and successful relationship with your Thai partner. Losing “face” could mean that you are barely able to pay bills and take care of your family. Because Thailand used to be a third-world country, and the highly materialistic nature of society, most Thais cannot afford to move down the social ladder, which is understandable to some extent.
Being able to maintain “face” and putting down food on the table is crucial to maintain a successful relationship is usually a vast majority might leave to find others that can. Love is a little more pragmatic in Thailand than in the rest of the world, and in most cases, you will be expected to financially support their parents to some extent, as the concept of family is drastically different between Thailand and foreign countries, part of the reason for this is that Thailand does not have a reliable social security system so if children don’t look after their parents, then who will.
If you can accept the fact that family is a Thai woman’s priority, and you do not mind helping financially here and there, they are likely to have a very successful and happy relationship with your Thai partner.
Although not specific to Thai girls, it is usually much more sensitive to them. In general, Thai girls tend to feel jealous much more easily than westerners. For example, hanging out with a female friend might already be a red flag, even though you might not think anything of it at all. They tend to assume the worst if a western man had a drink or even chats with another woman, which could lead to conflict and arguments because for you it might just be what it is, hanging out or just having a friendly chat with another woman.
The possible reasons for this are that Thai men are seen to be unfaithful, of course, it would be unfair to assume that all of them are, however, due to the widespread social acceptance of mistresses or “mia noi” in the past, there is some truth to the prejudice.
So you may be wondering if there's any solution to this... Of course, there is always a solution, you should avoid any eye contact whatsoever with any other girl at all cost! ... of course that was just a joke. Being honest is a good start, you should also let her know what she means to you and constantly tell her that you love her. You guys are probably used to that anyways.
Because Thailand is a Buddhist country, there is a taboo on sexual topics in Thailand. This is because views on women in Thailand are quite conservative, even though initially it might not seem like it. Because of the conservative nature of people, public displays of affection between couples are usually frowned upon, even for something as basic as touching, let alone kissing in public. This might be something to be aware of as in western countries, it is drastically different. So if your Thai partner seems uncomfortable with affectionate acts in public, it is completely normal and you should take things slowly and easily.