Learn Russian: Мы читаем трудные тексты.

It actually is in the accusative case! In Russian, for inanimate objects (things that aren't alive, like тексты), the plural accusative case looks exactly the same as the nominative plural. So трудные тексты is used both when it is the subject of the sentence and when it is the direct object.

Why does the adjective трудные end in -ые?

This is the standard ending for plural adjectives in the nominative (and inanimate accusative) case. Because the dictionary form of the adjective is трудный, you drop the masculine -ый and add the plural ending -ые to match the plural noun it describes.

Why does тексты end with -ы instead of -и to make it plural?

To make a masculine noun ending in a consonant plural, you usually add -ы. You only use -и if the word ends in a soft sign, -й, or if the last letter triggers a spelling rule (like к, г, or х). Since текст ends in a hard т, it simply takes -ы.

Can мы читаем mean both we read and we are reading?

Yes! Russian does not have a separate continuous tense like English does. The present tense verb читаем covers both general habits and actions happening right at this moment.