If you want to compliment someone on having done a good job doing something in Thai, you can say “เยี่ยม” [yîam] meaning “Excellent!” or you can emphasize it by adding the adverb of degree “มาก” [mâak] (very / extremely) -> “เยี่ยมมาก” [yîam mâak]. For example,
A: [phǒm tam project tîi naai mâwp mǎai hâi phǒm tam sèt léaw ná kráp]
A: Boss, I’ve finished the project that you assigned to me.
B: [yîam mâak]
Note that “ดีมาก” [dii mâak] (very good) can also be used but you won’t sound as excited, pleased or impressed with what someone did as if you said “เยี่ยม(มาก)” [yîam(mâak)].
However, rather than stating that a job is well done, Thai people tend to say that the person doing that job is good, talented or skillful, by using “เก่งมาก” [gèng mâak], especially when we compliment children. In everyday life, you will be much more likely to hear “เก่งมาก” [gèng mâak] than “เยี่ยมมาก” [yîam mâak] or “ดีมาก” [dii mâak].
A: “แม่ หนูสอบผ่านแล้ว”
A: [mâe, nǔu sàwp pàan léaw.]
A: Mom, I passed the exam!
B: [gèng mâak lûuk]
B: Good job, honey!