  We present Charles Translator, a machine translation system between Ukrainian
and Czech, developed as part of a society-wide effort to mitigate the impact of
the Russian-Ukrainian war on individuals and society. The system was developed
in the spring of 2022 with the help of many language data providers in order to
quickly meet the demand for such a service, which was not available at the time
in the required quality. The translator was later implemented as an online web
interface and as an Android app with speech input, both featuring
Cyrillic-Latin script transliteration. The system translates directly, compared
to other available systems that use English as a pivot, and thus take advantage
of the typological similarity of the two languages. It uses the block
back-translation method, which allows for efficient use of monolingual training
data. The paper describes the development process, including data collection
and implementation, evaluation, mentions several use cases, and outlines
possibilities for the further development of the system for educational
purposes.
