I was looking for SEO module for phpbb based forum and downloaded phpbb_seo module, followed the steps as mentioned in a thread.
Tried to install phpbb_seo module and went through as following.
# Have had the backUp of all files,
# Applied the mod code changes on copies of every file,
# Uploaded all the files through ftp,
# CHMOD the phpbb_seo/cache/ folder to 0777;
# Deleted all files of the phpBB/cache/ folder : just EXCEPTS the .htaccess.
# Went to mysite.com/forum/phpbb_seo/phpbb_seo_install.php and
Got Installation Error : >>>>>
Language file ./../language/en/mods/acp_phpbb_seo.php couldn't be opened.