Is it an error to leave out the to bach (circumflex)?
In words such as pêl (ball) or dŵr (water), is it a mistake to leave out the to bach (circumflex)?
That is, is it a formal spelling but pel, dwr would also be acceptable (a bit like "naïve" vs. "naive" in English, which are both possible)?
Or should the to bach always be present?
What about the ï letter which I've seen on the little "keyboard" beneath input fields? (In which words is it even used)? Can that be replaced by i or should it always be present?
Also, regardless of whether it's considered correct or not - does Duolingo accept mistakes that consist only of missing diacritical marks? (I know that for some languages, it's forgiving of missing marks, e.g. missing Turkish diacritics are ignored in the "English from Turkish" course, perhaps because many Turks taking it are on an English keyboard.)
yes, it is a mistake! circumflex, unlike some diacritics present in English, is not a relic from old times, or other language, and now irrelevant. it's a marker of vowel length. gŵydd ('goose') and gwŷdd ('loom') or mor ('so, as') and môr ('sea') sound differently, apart from having a different meaning. acute accent can be omitted because it only marks irregular stress pattern, e.g. nesáu ('to approach'). this can often be deduced without diacritics, like in this case - verbal nouns ending in -au are stressed on the last syllable.
Not sure about the welsh course but naïve is a French word, admitedly imported into English, like many other French words and phrases. However, the English alphabet does not use diacritics so in my opinion it remains a French word even if it is accepted in English sentences.
Personally, yes - I see it as a mistake; I teach that it should always be present and plays an important role in the spoken language, as do other accents. There was a great discussion had between myself and another contributor (all in good spirits :D) about whether or not to accept "rŵan" without the circumflex :P
I don't know the answer to your question, but I did wonder about the accents myself. The above Wikipedia article says 'the grave and acute accents in particular are very often omitted in casual writing, and the same is true to a lesser extent of the diaeresis. The circumflex, however, is usually included'.
The course does accept an answer if your only mistake is missing (or includiing unnecessary) diacritics. It seems to be a standard across the board with all languages.
Personally I would like it to get more critical as you progress - it's nice that it ignores it and just gives a nudge when you have just started to learn, but once you reach a certain level it should expect the learner to remember them (much as an actual teacher would!)
It is a mistake to leave out diacritic marks in all languages that have them. If Welsh is like Irish I assume they change the sound of the word and also the meaning.
With Duolingo you can leave them out, it will be marked as a typo. You can also leave out punctuation marks. So if it's easier for you to type that way then it's ok in that case to leave them out. I do it myself to speed up my typing. As long as you know it's not allowed in the correct written language.