Nice nicknames for sister in different languages

[Emely]

Hello,
I would like to make a present for my twin sister. For that I would like to no some nice nicknames in different languages from all around the world. It should be something like 'darling', 'sweetheart' or 'Schwesterherz', if you know what I mean. So, how do you (nicely) call your sister in your native language?
I know it could be difficult but I would really love to know it following languages: Icelandic (because we both love Iceland), Norwegian, Swedish, Finnish, Russian, Irish, walisian (?), French, Polish, Dutch, Czech, Portuguese, Spanish, Mexican, some Africa language (I'm sorry, I'm not into African languages), Hindi (Hindu?), Chinese, Korean, Thai (Thailand), Japanese, Tagalog (Filipino), Italian, Greece, ...

Of course is every other language welcome too!

Lovely greetings from Germany

[Bubulus]

In Spanish people just use the name of the person, or a diminutive/altered form of it. If her name is Patricia you can call her Patty... There's no equivalent of Schwesterherz.

[Linguaphile]

I agree with the above, but for the purposes of your project, one possibility for Mexican Spanish is mana (short for hermana, "sister") which is an informal way to refer to either a sister or a close friend. It isn't the most common thing to say to your sister, but it might work for your project.

In Finnish the normal word for sister is sisko. I'm not sure about other variations of it. I think that sisko itself is technically a diminutive form of sisar, but sisko is the normal, common word for sister, so I don't think it has any special positive or negative connotation.

In Estonian the normal word for sister is õde and the variation õekene is a diminutive form, something like "dear sister".

Just another suggestion if you have trouble finding enough translations of the type of word you are looking for, you might use translations of the word "twin" or "twin sister" too. In case you are interested in that, here are a couple translations:
Spanish: gemela (twin sister, for an identical twin); melliza (twin sister, for a fraternal twin)
Finnish: kaksoissisko / kaksoissisar (twin sister); kaksonen (twin)
Estonian kaksikõde (twin sister); kaksik (twin)

[h34]

In Latvian, the diminutive of māsa ('sister') is māsiņa, usually shortened to māsiņ when you address someone. So perhaps you could use māsiņ.

In Swedish you can say syrra instead of syster ('sister').

(I added question marks because I'm not a native speaker, perhaps there are better alternatives.)