Some carts are better at accepting patched roms than others.
The supercard for instance, althought the cheapest will not let you patch roms with translations easily. I've got it working, but I don't suggest it for beginners.
The best cart I've used is the EZF Advance (not to be confused with the EZ Flash Advance). I have their first cart and it only has real time clock support (for pokemon games) but it is by far the best cart I own. Their more recent generations are a lot better too, and can connect to a pc via a usb cable without the use of a gameboy (the earlier ones don't use usb and need a GBA or SP to work). When flashing a patched rom to the card the program asks if you want to remove the patch because it detects them. If you click on No it will flash the patched rom to the card, no problem.
Here is their website and what their products are. I highly recommend them.
Here's a list of carts and their compatibilities with GBMirco for reference.