These language text are defined in the language of JA Vega template: root/language/en-GB/en-GB.tpl_ja_vega.ini
; Portfolio Article Extra Fields
TPL_ABOUT_PROJECT = "About Project"
TPL_CLIENT = "Client"
TPL_DAY = "Date"
TPL_TYPE = "Type"
TPL_CATEGORY = "Category"
TPL_LINK = "Link"
TPL_RATE = "Rating"
You can override these language constants as you wish: https://docs.joomla.org/Help4.x:Languages:_Overrides