Functioning as the simple past tense and past participle of the verb "sweeten".
Definitions
Simple past tense and past participle of sweeten. She sweetened the lemonade with a splash of syrup.
Refined label: the adjectival use of “sweetened” is a past participle functioning adjectivally.
Translations
The sweetened tea was too sugary for my taste.
Подслащённый чай был слишком сладким для моего вкуса.
Definitions
Having had sugar or another sweet substance added to it. The sweetened tea was much more enjoyable than the plain version.
Made more pleasant or agreeable. The deal was sweetened with additional benefits to entice the investors.