Ignoring the whole druidic language thing: I have a better idea.
You want to learn druidic so your lore won't fall into the wrong hands. It doesn't prevent an evil druid translating it.
Instead, create a cypher. Obfuscate your writings, encrypt it. Then you're the only one who can translate it. No druid or wizard knows your own personal language. They'd have to decypher it, which, depending on the ingeniousness of your code, should be a lot more difficult than to hire a druid to translate these texts that have certainly not been written by a druid.