I have been through the English text files (en_GB - the default TestLink language) and corrected a lot of language mistakes and typos. I have also tried to clarify a few of the descriptions. It's not perfect, but I think it's a significant improvement on what we had up until now.
The files will be in the next TestLink release. In the meantime, if you'd like to try them now, I've made them available at http://sbpoley.home.xs4all.nl/testlink/en_gb.zip
Unzip the contents and copy the three files to your TestLink installation, directory: locale/en_GB.
I've tested the files with TestLink version 1.9.4, and briefly in 1.9.3. Probably they work fine with other recent versions as well, but I don't know that for certain.
Please let me know of any remaining errors or unclear passages which need improvement.
Improved English text available
Moderators: Amaradana, TurboPT, TL Developers