Farid said:
How do I add subtitles in BDtoAVCHD? It won't allow me to add anything :(
Never used BDtoAVCHD, but even if it doesn't allow you to add subtitles, you can still use it to create the AVCHD-compatible video stream.
Then just take the M2TS file created by BDtoAVCHD and demux it into its component streams using tsmuxerGUI. Then remux those streams again, including subtitles, using tsmuxergui and setting it to output AVCHD. The result will be an AVCHD with subs.