Pretend that directly in the middle of your character, there is a stick. your character has a front, back and sides.
By moving the stick forward. (Into a positive number) we move in that direction, because it is the primary vector for front to back movement.
And Right is classified as Positive, because right is the primary vector for turning, or applying velocity to the right or left.
Its sort of like putting a car in reverse I suppose?
This also simplifies the way you can describe, and respond to information in a game, Its happening on the right of the actor, because the vector is positive, so you know what your script will produce an effect to the right, as long as its based off character directional facing, and not the worlds directional facing.
To maybe answer your question, While Character directional Facing, and World directional facing do interact with each other, they are still independent of each other.
Your characters X axis, is that actors X axis, it can face any direction in the world. And you can use that directional facing to do things like line traces, without needing to reference the world. (technically not true, if you want to use that line trace for specific reasons.)