According to official documentation:
The Language property on a paginated report or a text box contains the locale setting, which determines the default formats for displaying report data that differ by language and region. If no value is specified for Language, Reporting Services uses the locale of the operating system on the report server for published reports or of the report authoring computer for report preview.
For more information on reporting locales, you can check out this documentation: Set the locale for a paginated report or text box.
You can also try changing your browser's language settings or your computer's regional settings.
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Aniya