Is it really 10 per cent on everything in Bulgaria?

No, and that shorthand misleads. Personal income tax is a flat 10 per cent and corporate income tax likewise 10 per cent under Art. 20 ZKPO. Sole traders pay 15 per cent. Dividends attract a further 5 per cent final withholding tax, for individuals under Art. 38 ZDDFL. For profit distributed to an individual that comes to 14.5 per cent in total, not 10. Social insurance contributions come on top, as does the question of which state has the taxing right in the first place. General information, not tax advice.