  A closely related point can be made in terms of translation. Translation of observation categoricals is quite unproblematic in principle. So we can count two theories as empirically equivalent not merely if they imply the same observation categoricals but also if they imply intertranslateable observation categoricals. So classical physics as formulated in English (say) would, by this criterion, count as empirically equivalent to classical physics as formulated in German, yet the two formulations are, strictly speaking, different theories. Quite generally, any theory is empirically equivalent to its translation into any other language. But this fact is also not of any great philosophical significance, and certainly poses no threat to realism.