This error pops up when installing the package from Package Control:

error loading meta info from Packages/Zig Language/Preferences/Comments.tmPreferences: Error parsing plist xml: expected < in file Packages/Zig Language/Preferences/Comments.tmPreferences on line: 1

It only pops up when you first install the package. Once you install it and manually select Syntax -> Zig the package works like expected without error. Looks like this error was introduced when making this package compatible with TextMate.