Is it just me, or do most all trading platforms spew complete garbage when it comes to forex volume? The volume bars on all charts seem to have different values and are even inconsistent within the same chart. It seems so highly unreliable that it's pointless to use any sort of volume based indicators or methods.
It isn't just you. Spot forex has no centralized exchange, and therefore there's no way of monitoring or recording volume. The only information that a spot forex "broker" can convey on this subject is their own volume, which is basically useless garbage, as you've rightly commented. There's nothing to stop one from using the volume of the front month's equivalent forex future as a substitute, though (and it can be a very good substitute: I've tried it, myself, in the past), but this then begs the obvious question "Why not simply trade the futures, instead?" for all their other advantages in addition to the availability of volume.
it is impossible to get the actual trading volume on the spot forex market. reason is that the market is decentralized. Spot forex brokers only show the volume based on their client's position.