Not the parent commenter, but -- days of week in Polish are a nice example, IMO.

`Środa` means `Wednesday`, but depending on the grammatical case it's going to be translated either to `środa` or `środę` (or five more, but somewhat less likely to appear in UI [1]).

- Next <Wednesday> is 2018-01-03. = Najbliższa <środa> przypada na 2018-01-03.

- This event happens on <Wednesday>. = To zdarzenie ma miejsce w <środę>.

If you mix the variants, it's going to sound very off (but it will be understandable, so there's that).

What's more, days of week have different genders, which affects qualifiers:

- <this> Wednesday = <ta> środa (Wednesday is a "she")

- <this> Monday = <ten> poniedziałek (Monday is a "he")

... together with the grammatical cases affecting the qualifiers:

- <This> Wednesday is crazy. = <Ta> środa jest szalona.

- <This> Thursday is crazy. = <Ten> czwartek jest szalony.

- I'm busy <this> Wednesday. = Jestem zajęty w <tę> środę.

- I'm busy <this> Thursday. = Jestem zajęty w <ten> czwartek.

[1] https://en.wiktionary.org/wiki/%C5%9Broda

This is fascinating, thank you. The intricacies of languages is so interesting. I especially love the insane way we danes spell out numbers.

59 == nioghalvtredssindstyve

59 == 9 [ni] + [og] ((3 [treds] - 0,5 [halv]) * [sinds] 20 [tyve])

So 9+2,5*20 == 59

Halvtreds means half third, or halfway to three. There's also halvfjerds and halvfems for 3,5 and 4,5. Exercise: spell out 79.