There are multiple ways to do this:
1. Add multiple columns to the table with the strings you have to localize. E.g. one column for German, one for English, and so on. And then get the string from the appropriate column. This is perfect if the number of languages stays more or less constant (you have to change the DB for every new language).
2. Add a translation table, with language, lockup and translation columns. So for every string you'll have multiple rows (one for each translation). This is good if the amount of languages changes/should be configurable.
3. Instead of the table solution, you could also lookup your string in a .po file.
But all of those need a little work and you have to have the option to change the way your db strings are read.