At this point you should be able to do any translation with ease. There should be only one instance of a label in all translation files and labels should be, as much as possible, prefixed by the application name.
If you are looking for how to translate Products or Categories Name and Descriptions, have a look at How to localize Product and Categories descriptions
To intialize the Label Manager in Webtools, before using "All files" option, 1st select a file and make a search. Then you will be able to select your language and all other options. This should be fixed one day...
Guide to OFBiz-i18n, Internationalisation of OFBiz