If you just want to test that you're "doing it right" (not necessarily test that your translations match up with things shown in-game in a particular locale's client) you can simply remove the locale check in your translations.
For instance, if your translation code looks like this:
local LOCALE = GetLocale()
if LOCALE == "deDE" then
L["Hello"] = "Guten Tag"
elseif LOCALE == "frFR" then
L["Hello"] = "Bonjour"
L["Hello"] = "Hello"
Then you could simply change the value of the variable LOCALE to the locale you want to test.
If you're using AceLocale, then if you're not getting any errors from that library, your translations are "working", and you should just release your addon. People who actually play in the locale and speak the language will let you know if there are any problems.