Irish is somewhat similar to how @jeinzi@discuss.tchncs.de describes German.

-ín is a diminutive added to the end of a noun. So for example you can have:

• buachaill (boy) → buachaillín (little boy)
• bóthair (road) → bóithrín (small road; this one has undergone some mutation because it's such a common word)
• smidir (fragment) → smidirín (small fragment, hence the English word smithereens)

Beag is the word that literally means small, and there are slightly different connotations. Buachaill beag is a boy who is small in size, while buachaillín is a term of either affection or derision depending on tone of voice. Bóithrín specifically means a winding country road with unkempt vegetation on the side, while a bóthair beag would be any small road.

Adjectives do not affect the words they are attached to. For example, the Irish word for red is dearg. Hence, a red rose is simply róise dearg, and a little red rose would be róisín dearg, though róisín is rarely used for flowers; it's basically exclusively a name. If you're talking about a flower, you'd be much more likely to say róise beag dearg, though róise dearg beag would also be correct.

Adjectives, however, can be altered by some adverbial prefixes, such as an- (very) and ró (too [much]). So, for example, very small is an-bheag, while too small is ró-bheag. (The BH there is pronounced like the English V. It can also be pronounced as W. I know the rule has to do with which vowels are adjacent, but I can't articulate what the rule is).

The past tense of many verbs is formed by changing the initial letter. Cuir, (put), for example, becomes chuir (put [in the past]); CH here is pronounced the same as in German, which is like the sound J makes in Spanish. Negation also tends to change the first letter of a verb; for example, cuireann (puts) → ní chuireann (does not put).

I know nothing about Irish, but this reminds me of the diminutive in German. There it would be

Rose - Röschen (little rose)

and likewise

• Brot (bread) - Brötchen (small bread)
• Haus (house) - Häuschen (small house)
• Katze (cat) - Kätzchen (little cat/kitten)

You could also translate "little rose" word by word as "kleine Rose".

The sole purpose of this grammatical form is to make something sound smaller, so you can't extend it to other adjectives like "red". "Little red rose" could be "kleine rote Rose" or "rotes Röschen".