Translation:We are on our way to Earth.
It seems this sentence will only accept "We were in the middle of a trip to Earth". I understand that it probably shouldn't accept "we were/are/will be going to Earth (to distinguish "-lI'" from "-taH"), or "we were/are/will be on our way to Earth" (to distinguish "lenglI'" from "jaHlI'"), but shouldn't it accept "We are/will be in the middle of a trip to Earth", or "We were/are/will be on a trip to Earth"?
English does not distinguish between the Klingon meanings of -taH and -lI'; only context does. In the middle of doesn't distinguish this at all. I can be "in the middle of listening to music," and it doesn't imply that I'm making progress toward the goal of finishing listening to music. The "progress" sense of the Klingon comes from the notion that you're traveling toward a goal.
If this sentence requires "in the middle of" instead of just "traveling," then this is just wrong.
with the very many small words being presented in the Klingon-to-English drag-and-drop translation exercise I had a real problem constructing a sentence that made sense. I've reported this and suggested you make "we were traveling to earth" the main translation for this reason.