translation override from skin bypasses llng.ini

Concerned version

Version: 2.0.14

Summary

• In lemonldap-ng.ini:

[portal]
error_9=Error 9 from llng.ini
error_13=Error 13 from llng.ini

• In templates/bootstrap/all.json:

{
	"PE13": "PE13 from all.json",
	"PE14": "PE14 from all.json"
}

Expected result:

• PE9 is translated as Error 9 from llng.ini
• PE13 is translated as Error 13 from llng.ini
• PE14 is translated as PE14 from all.json

Actual result (in HTML pages):

 "trOver":{"all":{"PE13":"PE13 from all.json","PE14":"PE14 from all.json"}},

Two issues:

• Skin file overrides llng.ini
• llng.ini is completely ignored when skin file is present

Possible fixes

trOverCache needs work, see also #2772 (closed)

However, changing current behavior might cause issues during upgrades if llng.ini contains test error messages