Answer
Yes, both existing built-in report text and custom strings you add yourself can be translated. For existing/built-in text, use the Translation Manager's Text Translations window, search for the relevant report's translatable text entries, and add a value in the Translation column for each target language — the translated text is used automatically when the report is printed in that language. For strings you've added yourself, they need to be defined in the report's .report model file, in its Report Texts section — this generates the corresponding .xsd schema plus supporting .rdf report logic, and you then need to make sure those text entries are also included under the .rdf file's report registration section. Once registered that way, the newly defined text appears under the Translations node in Report Designer and can be translated the same way as built-in text.