Read this: Burmese, the mother tongue of the Bamar and official language of Myanmar, is related to Tibetan and Chinese language. It is written in a script consisting of circular and semi-circular letters, which were adapted from the Mon script, which in turn was developed from a southern Indian script in the 5th century. The earliest known inscriptions in the Burmese script date from the 11th century. It is also used to write Pali, the sacred language of Theravada Buddhism, as well as several ethnic minority languages, including Shan, several Karen dialects, and Kayah (Karenni), with the addition of specialised characters and diacritics for each language.

From when are the  first impressions of the visually displayed language ?
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The earliest known inscriptions in the Burmese script date from the 11th century.