"It is not windy."
Translation:Chan eil i gaothach.
I guess (because you did not give any context to your comment, I cannot know where you did need to put ann at the end) you mean as opposed to sentences like tha cat ann there is a cat.
The verb tha is needs a ssubject (the one who is being described) and a predicate (something that describes them/it), not unlike English is.
In the sentence tha cat ann there is a cat the meaning is that a cat exists, cat a cat is the subject and the verb needs a predicate, and to state a general existence Gaelic uses ann there – again, similarly to English, but English changes word order (there is a cat vs regular a cat is there) while Gaelic does not. In some other languages such dummy predicate wouldn’t be needed, but Gaelic requires it.
In this sentence, though, you already have both a subject and a predicate:
- chan eil is not – the verb,
- i she, it (ie. the weather) – the subject,
- gaothach windy – the predicate.
Chan eil i gaothach it is not windy, i it is the subject being described, gaothach windy is the predicate describing it, there’s no place for dummy ann left here.
(Actually here the subject i is kind of a dummy subject referring to general conditions around, again it works similar in English and Gaelic, but eg. in Polish the sentence would be just nie jest wietrznie, literally is not windy without any explicit subject stated).
Might interest some people, I’ve just found it – this i referring to weather is explained by Roibeard Ó Maolalaigh in his Scottish Gaelic in Twelve Weeks as coming from a reference to feminine oidhche night instead, rather than to the weather words (thus I guess a while ago people would say tha e brèagha during a day and perhaps tha i brèagha during night time, later i becoming more popular in some dialects, as taught in Duolingo) – this would be in line with Irish still generally using masculine sé when referring to weather.
Scottish Gaelic in Twelve Weeks, §5.43 The Weather, p. 62:
43 The Weather
The weather sìde (f) or aimsir (f) is an important part of daily conversation in Gaelic. Most conversations begin with comments on the weather. Here are some useful examples:
- Is e latha brèagha a tha ann. It is a lovely day.
Alternatively, we can simply use the verb tha as follows:
- Tha e brèagha an-diugh. It is fine today.
The feminine pronoun i rather than e is used in some dialects to refer to the weather in the above phrases; the feminine reference refers to, or originally referred to, oidhche ‘night’ which is a feminine noun.
The sentence needs a subject (the it in English it is not windy), it can either be i (the feminine pronoun, she) or e (masculine, he). In Gaelic the words for weather (sìde, aimsir) are feminine, so feminine pronouns are commonly used when speaking about weather.
Though I think one can also encounter chan eil e gaothach in the Gàidhealtachd, as I think sometimes e is also being used when referring to weather conditions (as is in Irish: níl sé gaofar), perhaps because là ‘day’ is masculine.