problem solved:
void gameWindow::setTextProperties(sf::Text &text, std::string string, unsigned char_size, sf::Color color, sf::Font font, sf::Vector2f position, float angle, sf::Uint32 style)
to:
void gameWindow::setTextProperties(sf::Text &text, std::string string, unsigned char_size, sf::Color color, sf::Font &font, sf::Vector2f position, float angle, sf::Uint32 style)