Learn German: Heute ist der zwanzigste Oktober. - Today is the 20th of October.

For numbers from 20 upwards, German adds the suffix -ste to the base number. So zwanzig (twenty) becomes zwanzigste (twentieth). For numbers 1 through 19, you usually just add -te.

Why does it end in -e (der zwanzigste) instead of -en (zwanzigsten)?

Ordinal numbers take normal adjective endings. Because we are saying what today is using the verb ist, the date is in the nominative (subject) case. After the nominative masculine article der, the ending is just -e. You would use -en if you were saying something happens 'on' a date, which requires the dative case (like am zwanzigsten Oktober).

Why isn't there a translation for the word 'of' in the German sentence?

In English we often say 'the 20th of October', but German doesn't use a preposition there. You just put the ordinal number directly before the month, treating it like a normal adjective describing the month.

Why do we use the masculine article der here?

In German, all days of the week, months, and seasons are masculine nouns. Since we are talking about Oktober, the matching article is der.