Does anyone think that "gets filled" should also be accepted? NOTE: If the English version with "is filled" is given to be translated into Irish (or other language) it is potentially ambiguous since it could refer to an action that gets done to the bottle, as in this example, or the resultant state (ie it has been filled and is now full).
Exactly. The Irish autonomous (“passive”) form always specifically refers to an action, not a state. In fact, the best translation of this sentence would be “Someone fills the bottle with wine”. Of course, “is filled” is just fine as well, but so is “gets filled”, which should be accepted as well.
The point of IuileanMGabhann argument is that the saorbhriathar is not actually passive - there is an agent (whether "someone" or "something"), but that agent is not relevant and not identified. English uses the passive voice when it wants to avoid identifying the agent, though in the case of English, you can have the "passive with agent" when the agent is identified with "by" (the bottle was filled by the sommelier" is in the passive voice, "the sommelier filled the bottle" is in the active voice).
Some people insist that "voice" is important, and that you should translate the saorbhriathar with a non-specific agent, such as "someone" (or, God between us and all harm, "one"), but Líonann duine éigin an buidéal and líontar an buidéal are very definitely not equivalent in Irish. Not only does the saorbhriathar allow for a machine to do the filling, it also allows for a non-corporeal being, or the weather, or even magic - the agent is not relevant.
Only masculine nouns starting with a vowel, and only after the singular definite article an, not the plural definite article na, and only in the nominative case, not the genitive or dative. (And, for the purists, the accusative case, as it follows exactly the same rules as the nominative case in Irish).
tá an t-úll aibí - "the apple is ripe" (nominative singular)
tá na húlla aibí - "the apples are ripe" (nominative plural)
d'ith mé an t-úll - "I ate the apple" (accusative singular)
d'ith mé na húlla - "I ate the apples" (accusative plural)
blas an úill - "the apple's flavour/taste" (genitive singular)
blas na n-úll - "the apples flavour/taste" (genitive plural)
ar an úll - "on the apple" (dative singular)
ar na húlla - "on the apple" (dative plural)
Because líontar refers to the action of an unnamed subject filling the bottle, not the state of the bottle after that unnamed someone has filled it.
In English, when you want to avoid mentioning the subject of a verb (the person doing the action), you use the passive voice. In Irish, you use the saorbhriathar.