Putri Duyung (1985)

I think it's a reasonable guess that this Indonesian film Putri Duyung (The Mermaid) was inspired by Splash, seeing as it came out a year later and features a mermaid who goes on land to find a man that she's in love with, despite not knowing human social norms or how to speak his language, and whose tail transforms upon contact with water. At the very least the bathroom scene where Intana frantically uses a hairdryer to dry her tail while Tintus bangs the door, is right from Splash.

Central concept aside, this film is more a titillating and in some places very violent action movie with extended beat-'em-up scenes thanks to Tintus' propensity to antagonize some criminal-type folks. Eva Arnaz is Intana the mermaid and Barry Pima is Tintus, the man she falls in love with, and they have some comedy moments early on before Intana learns how to communicate with him.

There aren't any underwater scenes but Intana isn't the only mermaid we see, as there are other mermaids of her clan, plus a Mermaid Queen who gives Intana permission to go to land, albeit on the condition that she return. At the end of the movie and after an extended fight scene where Tintus fights the bad guys who've kidnapped Intana, Tintus learns the truth about Intana, and she declares that their worlds are too different and they must follow their own destinies, ending in a separation for the lovers.