oh it's simple, download ttarchext:
http://aluigi.org/papers.htm#ttarchextnow you must launch it from the console or you must prepare a batch file (file.bat) to run it:
ttarchext.exe 28 c:\file.ttarch c:\output_folder
so it will extract all the files contained in file.ttarch (for example CSI5_Miscellaneous.ttarch) into the c:\output_folder (which must be empty).
I'm not a modder but I guess that the files containing the language strings are those with the langdb extension.
now the rebuilding process depends by the game so take the following only as a generic example.
delete all the files in output_folder that you have not modified and launch:
ttarchext.exe -x -b -V 8 28 c:\0.ttarch c:\output_folder
it will create the file 0.ttarch that you can place with the others ttarch archives of the game and should be loaded by the game.
if the game crashes remove the -x option from the previous command.
if the game doesn't load the new modified files then I guess you must rebuild the whole archive or giving it another name.
note that I can't help with modding stuff or info about the content of the extracted files, I work only on ttarchext
