I find it in the src file,seems Ubuntu haven't update the game for a long time

Yep, update your Ubuntu first or compile the latest release (you shouldn't use 0.9.12 if you want to play online with many others; so pick 0.9.11).

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If you notice missing or wrong translations or you think something should be renamed and/or updated:

There are 3 files for each language within the following folder (data directory; not sure about exact location in Ubuntu right now):
[...]\share\hedgewars\Data\Locale

The following files contain the texts used by the game - replace # with your locale (for chinese either zh_CN or zh_TW - depending on what you want - traditional or simplified):

#.txt -> Edit those strings used by the engine (the game itself) with your favourite text editor.
hedgewars_#.ts -> Edit the strings inside this file with your favourite text editor but be sure to not modify text that shouldn't be translated (like paths, text etc.) The changes you do here won't be used by the game until they're "compiled" by a special tool provided by qt (lrelease).
hedgewars_#.qm -> The compiled ts file used by the frontend (setting up the game, etc.)

As you mentioned .po files i'm sure you're able to understand the basic concepts/file contents, so I won't explain those.

If you made changes/corrections you'd like to share with others, post them here on the forums and they might be included in future versions.

Allarem, also, both zh_CN and zh_TW already exist (admittedly perhaps a little out of date, especially zh_CN).

Is your locale not set to one of those?
You might try creating a hedgewars shortcut that is:
LC_ALL=zh_TW.UTF-8 hedgewars

Oh. Heh. I missed the part where he said he was out of date.

Anyway, zh_TW was definitely updated a great deal for 0.9.12 - hopefully http://www.getdeb.net/app/Hedgewars
will add the .12 build soon.