iShares Core € Govt Bond vs Xtrackers II Global Government Bond

They track different indices: iShares Core € Govt Bond follows Bloomberg Euro Treasury and Xtrackers II Global Government Bond follows Bloomberg Global Aggregate Government. They also differ in cost (0.07% vs 0.25% TER), replication (physical vs physical) and domicile (Irlanda vs Luxemburgo).

Nobody can know that: they track different indices, so their returns will diverge, and past index performance is not a prediction. What you can control today is the cost, the tax structure and whether the index actually covers what you want exposure to.

iShares Core € Govt Bond has the lower annual fee. Applying the same 7% gross return to both with €300/month, that fee gap alone is worth about €3,379 after 20 years — that part is arithmetic, not a forecast.

Both are distributing, so on this point there is no difference between them.

Yes. Unlike two funds tracking the identical index, these give you genuinely different exposure, so holding both is not automatically redundant — just be aware you may end up overlapping on the largest companies and doubling your rebalancing work.