feat(startscreen): change ui texts from german to english and fix button click event

src/button.py

@@ -45,6 +45,8 @@ class Button:
             current_color = self.hover
 
             # check if left mouse button is pressed
+            if pygame.mouse.get_pressed()[0] == 1:
+                self.clicked = True
             if pygame.mouse.get_pressed()[0] == 0 and self.clicked:
                 self.clicked = False
                 action = True