It's working correctly. The English string is "Your current %s" with language key "YOUR_CURRENT_S_8e539b" the word "Subscription" comes from your configuration. Specifically "Singular name for subscription/membership" and "Plural name for subscriptions/memberships".
The language key "YOUR_CURRENT_SUBSCRIPTION_47e482" and language string "Your current subscription:" are only output in the CBSubs module as the "Intro of current subscriptions" parameter.