The general back end search box includes language strings within the scope of the search. You can find language strings with a partial text match on either the name of the string or the value. For example, searching for 'street' will find any language string that includes the word 'street' within its value (the visible text you see on the front of the site) or its name (for example, ContentText_StreetAddress).

If you navigate to the language strings page, you have more powerful search tools. Go to 'Regional Settings > Language Strings'. You can filter the search to a particular language, or to only search for the submitted text within the value, name or class. You can also filter by whether a string is used on the front or back end of Kartris.