OET interlinear REV 11:19

uW Translation Notes:

Note 1 topic: figures-of-speech / activepassive

ἠνοίγη ὁ ναὸς τοῦ Θεοῦ ὁ ἐν τῷ οὐρανῷ, καὶ ὤφθη ἡ κιβωτὸς τῆς διαθήκης τοῦ Κυρίου ἐν τῷ ναῷ αὐτοῦ

˓was˒_opened_up the (Some words not found in SR-GNT: Καί ἠνοίγη ὁ ναός τοῦ Θεοῦ ὁ ἐν τῷ οὐρανῷ καί ὤφθη ἡ κιβωτός τῆς διαθήκης αὐτοῦ ἐν τῷ ναῷ αὐτοῦ καί ἐγένοντο ἀστραπαί καί φωναί καί βρονταί καί σεισμός καί χάλαζα μεγάλη)

If your language does not use these passive forms, you could express the ideas in active form or in another way that is natural in your language. Alternate translation: [God opened his temple in heaven and I could see the ark of the covenant of the Lord in his temple]

Note 2 topic: figures-of-speech / metonymy

ἠνοίγη ὁ ναὸς τοῦ Θεοῦ ὁ ἐν τῷ οὐρανῷ

˓was˒_opened_up the (Some words not found in SR-GNT: Καί ἠνοίγη ὁ ναός τοῦ Θεοῦ ὁ ἐν τῷ οὐρανῷ καί ὤφθη ἡ κιβωτός τῆς διαθήκης αὐτοῦ ἐν τῷ ναῷ αὐτοῦ καί ἐγένοντο ἀστραπαί καί φωναί καί βρονταί καί σεισμός καί χάλαζα μεγάλη)

By this expression, John likely means by association that in his vision, God created some opening that allowed him to see into the temple of God in heaven. If it would be helpful in your language, you could use an equivalent expression or express the meaning plainly. Alternate translation: [God allowed me to look into his temple in heaven]