The thing is some Orthodox today argue against modernizing liturgy, insisting on "old" languages like ecclesial Greek and church Slavonic as opposed to modern Greek, Russian or English.
The Russian Orthodox Church came very close to translating its liturgy into, if not the vernacular, at least something closer to modern Russian. However, the events of 1917 sidetracked that when the puppet church set up by the Communists (the Living Church) used modern Russian, so the Russian Orthodox Church kept with the old tradition to avoid looking like it was comprising with modernity.
Some minority peoples of Russia had the liturgy in their own tongue, such as the Komi. Unfortunately, these liturgies are no longer permitted in the Russian Orthodox Church, but the reason for that is the Kremlin's desire to wipe out minority cultures, not any theological issue.
The Greek Orthodox Church continues to use Byzantine Greek, incomprehensible to the ears of many. When you are speaking with your modern language's sound system a language that had a rather different sound system, what can you expect besides confusion? In any event, the maintenance of archaic Greek in the Church is understandable when the entire educated Greek population maintained archaic Greek as the country's written norm until the 1970s.
So basically the reasons for retaining the old languages are, at the official level at least, inertia and politics, not theology. You will encounter plenty of simple churchgoers claiming that the old languages must be retained because they are especially holy, but this is the Heresy of the Trilinguals that was spectacularly refuted by St. Cyril some 1200 years ago.