And care to elaborate on what you mean by song flow? As long as the lyrics fit the syllables or progression of notes in the song, I always felt songs written with that goal in mind flowed well. The only thing that ruined that was awkward wording or clumsy placement of specific words/lyrics in my experiences.
I think I'm talking about what you're talking about, but let me clarify. Sometimes, you can get the syllable count right, and you can stop your English phrases when they stop... but then, well I noticed a few things at least.
(Disclaimer: Not a literal translation. I think and I think you think it's best not to even attempt one.)
(Tonari ni...)
待ち続けたあの場所に君は -> And in this same old place, I watch and wait and cry for you
At "old place," I feel the song stops a bit in English (at "old"), where it doesn't in Japanese. There's a small hiccup, and given how I think the song flows, my voice doesn't want there to be one there.
And even when I was staring at a rough draft of this translation, I thought about singing it. Even if they were well enough made that I didn't get the "What am I singing?!? This doesn't even make sense!" feeling, I think at one point I realized that the emotion that I thought should be in the song... I, personally, could not deliver with the English lyrics I was thinking of. To adapt a famous quote, it was like, "Cael, you can write this stuff down, but you can't sing it!"
Which means, of course, I had to find other lyrics... and what I think up of sometimes makes me question if I'm really doing this right.