- 'Different' doesn't mean 'better' or 'worse'.
- 'British' doesn't necessarily mean 'older' or 'original'.
- 'Older' doesn't mean 'better' either!
- Let's enjoy each other's dialects AND our own!
First: 'Different' doesn't mean 'better' or 'worse'. Thailand is fiercely proud of its independence. Particularly, they are rightfully proud of the fact that Thailand is the only Southeast Asian nation never to be colonized or occupied by a Western nation (note the word Western--Japan occupied Thailand in WWII, and don't forget earlier history, when Thai เมือง (city-states) were เมืองขึ้น (vassal states) of the Khmer empire*). As a result, they are defensive against the encroachment of foreign culture. This is problematic, because the modern "Thai" culture has been shaped and constructed and subsequently manipulated as a political tool in the last 60 years. The idea of "Thainess" (ความเป็นไทย) as a contrast with everything else is still strong, and still invoked regularly for innumerable causes. Minority languages and cultures that are not part of the "Thai" tradition may never receive full legitimacy. I'm reminded of the Mokken sea nomads in the Southern islands, who are native speakers of a Malayo-Polynesian language, and whose children are now being taught Thai in their island classrooms, complete with pictures of the king and queen at the front of the class, like every other classroom in the country. Nevermind that the ancestors of the Mokkens were in the region centuries (millennia?) before the ancestors of the Thais. I wonder if the irony of this is lost on everyone.
I, like Lynneguist, believe that different is not necessarily bad. Many people in Thailand are very good at manipulating popular sentiment by acting as alarmists. There is a neverending stream of newspaper articles about ภาษาเสื่อม, ภาษาวิบัติ, ภาษาสแลง, ภาษาวัยรุ่น and all the other examples of "corrupted language" out there. But change happens. It's natural. And youth slang doesn't mean the downfall of society. If it gains larger legitimacy, then it's no longer youth slang.
If there is influence from foreign languages, it doesn't mean Thai culture is in danger of extinction, nor the language. This ultra-nationalist bent has been going on for at least 60 years. Back then, it was the economically-dominant Chinese who were vilified. Field Marshal Plaek Phibulsongkhram (จอมพล แปลก พิบูลสงคราม) was Prime Minister (and one of many military dictators in Thai history--post-coup government included) from 1938-1944 and 1948-1957 (he was overthrown once by one of his generals, but managed to came back into power, later to be ousted again and eventually die in exile in Japan). He was extremely Sinophobic. In the 1930s, the state created corporations to take over production of commodities like tobacco and petroleum from Chinese immigrants, and Chinese-owned businesses were subject to more control and taxes than Thai-owned businesses. This was part of a campaign to use only Thai-made products, because the Chinese hold on the market was too strong. He mandated that all Chinese schools must either switch to instruction in Thai or close. In a 1938 speech, one of his right hand men (in)famously compared the Chinese in Thailand to the Jews in Germany. In some ways, this is just a trend that has never died. In other ways, it's cyclical. Last time it was the Chinese. It has also previously been the Khmer and the Burmese. This time it's the generic ฝรั่ง, the Westerner.
Second: 'Thai' doesn't necessarily mean 'older' or 'original.' This may be a touchy spot. Much of the ราชาศัพท์ "royal speak" of Thai, used in reference to royalty/deity, is borrowed from Khmer, because Khmer was the court language (ภาษาราชการ) when the several Thai groups were vassal states of the Khmer empire. Therefore, Khmer words gained prestige and became associated with royalty. The language is a product of its environment, and its development includes centuries or millennia of contact with Khmer, Chinese and other civilizations and their languages. Sometimes a borrowing is very, very old! Old enough that it "feels" Thai, and is thus not considered a foreign borrowing anymore. When modern youngsters complain about the vast amounts of hard-to-remember and hard-to-understand Indic loanwoards from Pali and Sanskrit, they are told by their Thai teachers that Sanskrit words are Thai words now. We shouldn't look at them as loanwords, but just accept them as Thai.
Third: 'Older' doesn't mean 'better' either! The Thais should recognize this, because they reject older native words like กู and มึง (which everyone knows were used in the Sukhothai era), in favor of words that are often borrowed. This ties in with the second point. The history is complex, and contact and mutual influence has been going on for thousands of years.
Fourth: Let's enjoy each other's dialects AND our own! Contrary to popular belief or understanding, every speaker of a language speaks a dialect (ภาษาถิ่น). The idea of a "standard" language is a myth (English speakers don't understand this either). Standard language is an idealization that only exists in books. No one speaks Standard Thai natively. When most people say "Standard Thai", they usually mean either "textbook Thai" (the idealization) or "Bangkok Thai" (the closest realized form). But Bangkok Thai is a dialect just as full of regionalisms as ภาษาอีสาน, ภาษาเหนือ and ภาษาใต้, and any other regional variety of the language. Bangkok is a ถิ่น, so Bangkok Thai is a ภาษาถิ่น. Simple as that. But because the majority of television and radio communication is done in Bangkok Thai, the idioms and regionalisms become more widely known, and thus are seen as part of the "standard" language.
I don't have a problem with using the phrase Standard Thai or Standard English, though. I would propose, however, that we use it to mean a given language, allowing for certain variation based on majority use. We can call "drinking fountain" standard English, but "bubbler" is probably regional English. Likewise, มะละกอ is Standard Thai, while หมากฮุ่ง/หมักฮุ่ง/บักฮุ่ง are examples of regional Thai (but may be "standard" parts of their respective dialects).
In linguistics, there is the concept of an idiolect. That is, the language that you (and you alone) speak. No two people have the same idiolect. I can't find a word in Thai for this, so I'm going to propose ภาษาประจำตัว or, as an Indic-derived alternative, สวภาษา [สะ-วะ-ภาษา], meaning ภาษาของตนเอง "one's own language". If you speak Thai, at any level, then you have a particular Thai ideolect. If we recognize that no two people really speak the same language, and that language is conventionalized (oral) symbols standing for concepts, then we begin to see how arbitrary it really is. And how quickly it can change. "Bad words" become acceptable, neutral words become "bad words," borrowed foreign words become "native", new words are coined, and other words fall out of use.
None of this is to say that anything goes. Of course there are certain word orders that are grammatical, and others that aren't. Of course there are certain words that are inappropriate in one context, and appropriate in another. I'm not saying everything is correct (I find a lot of eggcorns just as annoying as the next guy). It's important that we have standards and conventions to ensure that we understand each another! But at the same time, we can appreciate the vast variety of language, without fooling ourselves into thinking that there is such a thing as a pure language. And this holds equally for Thai, English, and every language.
*Some Thai historians justify this by claiming the ขอม Khom, which is the term the Thais use to refer to the Khmer people of that area, weren't really the ancestors of the modern Khmers, but rather the ancestors of the Thais themselves. This is nationalistic nonsense. That Thais today still use the word Khom, a term of dubious origin, shows that they still don't want to admit that the Khom of yesteryear and the Khmer of today are related.