Ok because ki4m translated HU for the us version into german I will also do so and follow these steps:
To get at the .tbl files.
Download
WinMPQextract somewhare and run the program
1: Once its running, click "Open" and navigate to your d2 base folder.
Select d2data.MPQ first and open it.
2: Along the top of winmpq you will see a dropdown menu. Select the dropdown and select the ".tbl" option. Now hit enter.
This will show only the .tbl files.
3: The one you want from this file is data\local\lng\ESP\string.tbl.
Highlicht it then click extract and pick somewhare to extract too. This will create a data folder wharever you extract it too with the .tbl in data\local\lng\ESP.
Once youve done that. Do the same for d2exp.mpq. the file you want this time is in the same location as before but is named "expansionstring.tbl"
Extract it to the same location as before (along with any "string.tbl" that may or may not be there).
Finally, open patch_d2.mpq (from a clean spanish d2 install) and repeat the steps above, only this time, the file you want is "patchstring.tbl" in the same location as the others (data\local\lng\esp\).
Extract to the same place as before.
You should have string.tbl, expansionstring.tbl and patchstring.tbl inside that extracted data folder now. Those have all the strings for ingame text.
Ki4m will explain the rest I hope
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Edit @ Ki4m: It might be a good idea might to make a spreadsheet/list of all the existing strings that need to be changed. Then a list of the strings that need to be added and post it in the original post so it can be done just by looking at the list and opening the .tbls rather than checking texts individually etc.
Then the owners of the german version of diablo are also able to use it ^^ (with german cinematics as well). It surely not really important but might be more compfortable for some people. When I am finished I gonna post it here in this section.