I have a Viking Husqvarna Ruby Royale mucho bucks, sews multi directional but for what you want probably not cost effective what about using the iron on hem tape to attach your stripes?

Sounds like a lot of trouble. If the pants are for infrequent wear, fuse the stripe on the pants. Put something inside the pant's leg like parchment paper before fusing.

My first high end babylock did it and it was about 1800

Since you are new to sewing, take our advice, open up the inter seam from crotch to hem, lay the pants leg flat, pin the "ribbon" down the outside seam, centering it. Sew from top to bottom, re-sew inter seam, re-hem. Forgot to tell you, fold down the top ribbon by waist so you will not have a raw edge.

I agree with Patricia's advice. An alternative is to hand sew the stripes/ribbon to the side of the pants. I would probably choose the hand sewing option myself.

My Brother machine does this, it cost around $2000. I don't think you would be able to sew the stripes on using this feature unless the legs were very wide.

My Epic and my last 2 previous Vikings did that all directional stitch, I never have really used it, should try it someday. I have a fairly big harp but I don think a pants leg would fit nicely all the way on it. The advice to open the seam, seems the best !!!!

I have a Babylock Ellegante the sews both backwards and sideways. I've never used these stitches, only to try them out. My machine cost about $5000.00 but that was 11 years ago.

I have simply sewed the stripe on my sweats by hand.

My Bernina 1630, TOL about 20 years ago, sews a sideways stitch. I paid $550 on ebay.