Please provide an URL link to the official "Linux naming convention".

this is not "official" it is a convention, and you know surely better than I do that the system naming scheme on Linux has always used small letters without space.

[...]Typically, however, file names only use alphanumeric characters (mostly lower case), underscores, hyphens and periods. Other characters, such as dollar signs, percentage signs and brackets, have special meanings to the shell and can be distracting to work with. File names should never begin with a hyphen.

most people use all lower case. The reason is simple. Capital letters mean extra work. There is no way around it, each switch between capital and lower case means an extra hand motion, and an increased chance of user error. I can't count how many times I've hit Caps Lock instead of Shift, or Tab instead of Caps Lock. All lowercase is just easier.[...]

I can understand the "aesthetic" (not sure if the term is correct) concern for GUI users in naming the /home special directories with a capital Documents vs. documents, etc. but this can easily be reverted.

Empathy is one of rare software using a capital letter for its local configuration directory. If there is not particular reason, can I ask for a minuscule letter for the sake of the homogeneity (and CLI usage). Thank you.

No spec says anything about capital letters. Directories are in the right place per XDG.