Im pretty sure all the Legendaries are gonna keep their original names, or their gonna be romanized:
(Im not so sure these are legendaries, but I'll include them anyways)
Zorua- Retains the same name *CONFIRMED*
Zoroark- Retains the same name *CONFIRMED*
Victini- Victiny
Kobaruion- Cobalion or Cobalon
Terakion- Terrakion or Terrakon
Birijuon- Virizion or Viridion
Torunerosu- Torneros, Tornlos, or Tornelos
Baruterosu- Barteros, Bartlos, or Bartelos
Reshiram- Retains the original name *CONFIRMED*
Zekrom- Retains the original name *CONFIRMED*
Randorosu- Landoros, Landlos, Landelos, or Landolos
Kyuremu- Kyurem, Kyulem, or Kulem (I personally like Kyulem)
Kerudio- Keldio, or Retains the original name
Meroetta- Meloetta, Meloeta, or Meloida
Genosekuto- Genesect, Genosect, or Genisect (Again, I like Genesect, but thats just me.) Genesect probably is a portmanteau of Genesis (meaning 'Beginning') + Insect (hinting towards its figure)
Maybe???