וַתֵּשְׁב֥וּ בְקָדֵ֖שׁ יָמִ֣ים רַבִּ֑ים כַּיָּמִ֖ים אֲשֶׁ֥ר יְשַׁבְתֶּֽם׃
너희가 가데스에 여러날 동안 거하였었나니 곧 너희가 그 곳에 거하던 날 수대로니라
Rashi on Deuteronomy
ותשבו בקדש ימים רבים SO YE ABODE IN KADESH MANY DAYS — viz., nineteen years, as it is said here כימים אשר ישבתם, ACCORDING TO THE DAYS THAT YE ABODE, i.e. abode at all the other stations. They (the total years) were thirtyeight years; nineteen of them they spent at Kadesh, and nineteen years they went moving about aimlessly, and then they returned to Kadesh, as it is said, (Numbers 32:13) “And he made them move about in the wilderness”. — Thus have I found in Seder Olam 8.
Rashbam on Deuteronomy
כימים אשר ישבתם, another way of saying: “as you are well aware.”
Rabbeinu Bahya
ותשבו בקדש ימים רבים, “you remained in Kadesh for many years.” A total of 19 years. The words כימים אשר ישבתם mean as the total number of years you stayed in all the other locations. The subject is repeated in chapter 2 verse 14, where the number of years it took to get from Kadesh Barnea to the river Zered is given as 38 years. This number is confirmed in the Book called Seder Olam — "Nineteen years they spent in Kadesh and nineteen years they wandered the desert."