[Asiaplay]

I thought it was only used within the X-Cart add-on module "Gift Registry".

i.e. steps are like this
a) products are added to a customers "wish list",
b) then wish list can be added to a customers "gift list"...
c) then the customer adds "friends" names and e-mails to each "gift list" they have.
d) then those friends can come to your store and view that "gift list" (for that customer) - add comments or add those products on the gift list to the cart (i.e. view friends gift list.).

However that was as I remember, the language tag is "view friends gift list" (not lbl_view_friends_wishlist).
I see you are using V4.2.X (which I have not used yet) - perhaps in that version some code that exists (either on purpose or is there by error), which either relates to the gift registry add-on module (if the language variable is added or present) OR is a newer feature in V4.2.X, which works the same way as the gift list logic.

Cheers - Asiaplay

PS: I am wondering if you added a language recently, which includes these extra language tags (the language tag should just lie dormant i.e. not be used anywhere - but due to incorrect code in one template, this is suddenly causing this language tag to appear on a page).