Final answer:
The correct translation for 'Space Marine Legions' in Warhammer 40,000 terminology is 'Legio Astartes'. This term represents an elite group of genetically-engineered soldiers within the game's universe.
Step-by-step explanation:
The term that translates to 'Space Marine Legions' is Legio Astartes. These were the elite, genetically-engineered warriors in the fictional universe of Warhammer 40,000, a tabletop miniature wargame. The other terms listed have different meanings within the same universe: Frateris Militia refers to the militant arm of the Ecclesiarchy, Astra Militarum stands for the Imperial Guard which is the primary fighting force of the Imperium, and Collegia Titanica is the division that controls the massive war machines known as Titans.
The Roman legions, which may be a source of inspiration for many military science fiction organizations, were the principal military units of the Roman army. Commanded by a legate, each legion was made up of several cohorts, headed by centurions, and included a mix of heavy infantry and various specialized units necessary for sustained combat operations in the ancient world.