You have every right to criticize American culture, and yet, it certainly seems, that you would deny people the right to criticize non-American cultures.
You are only engaged in a double standard when you apply your sense of morality to judgments about Western culture but then argue that others cannot or should not when it comes to foreign cultures.
Everyone has a right to criticize practices they believe to be immoral and I would go further and say that everyone has an obligation to, in some way, see that those practices don't continue. When it comes to practices in foreign cultures, the only acceptable way to affect change is through education and persuasion, because doing so by force tramples the primary right of those who embrace the practice: Liberty.
Having said this, there are hypothetical practices that would test this principle for all of us. An extreme would be the ritual slaughter and cannibalizing of "unfit" infants and the elderly. One can imagine how a given culture could rationalize this practice, but very few people in the West would find it morally acceptable, and I feel certain that there would be public pressure exerted to put an end to it by any means. Whether or not governments bent to that pressure is another story. Slavery is another such practice and I know of no culture in the world who is proudly willing to advertise their embrace of it, because they know how most of the world considers it. Nevertheless, slavery continues in cultures throughout the world.
Within the so-called Western Culture there are differences on what practices are acceptable and what are not. The Death Penalty for example. European nations, by and large, find it to be immoral and unacceptable and do their best, within limits, to oppose our use of it. A prime example is their refusal to extradite someone in their country to the US without assurances that the person won't be executed. Have they stepped over your line? If, as I suspect, you also object to capital punishment, I doubt you will think they have.
When you argue for moral relativism and multi-culturalism and you wish to remain intellectually honest, you don't get to pick and choose the practices you get to condemn.