The descriptions of system internal debit types and credit types are not translatable from the GUI. We should make that work, as the descriptions are used for display for example on the cashup summary print outs (see bug 27779)
As this leaves no way for people to fix translations for their use but SQL, I'd consider this is in a grey area to be a little more bug than enhancement.
Pretty sure those were done this way at the time as a requirement.. if we allow them to be edited then the translations break from memory.
I think we use the codes for the translation in the templates, so this should be ok. There is an additional description that is English by default and can be translated via the installer files. But when we add new system internal debit types/credit types that are added via the database updates, the library has no means to translate them as well and they will be a mix of languages.
I think the description might be used in reports.