ELITE SAISHOU-SAMA NI HIROWARETANODE, DANSOU SHITE HISHO WO SURU KOTO NI NARIMASHITA

Tsugumi, a company president's secretary who finds her work her life's passion, is framed by a colleague and fired. In despair, she accidentally falls into a river and finds herself in 19th-century Vienna! Luckily, she is picked up by the handsome Chancellor Metternich and becomes his apprentice secretary on the condition that she disguises herself as a man! Using her past career experience and an electronic dictionary she happens to have with her, Tsugumi's work gradually earns her recognition in Viennese high society. But one day, her true identity as a woman is almost revealed to those around her...!? (Source: Starts Shuppan, translated) — Description from AniList community (anilist.co).