In a code language, YOGHURT is written as 251578211820. How will DEVELOP be written as in that language?

As per the given in the question,

$$ \ Y \ \underrightarrow{25 \ letter} \ 25$$

$$ \ O \ \underrightarrow{15 \ letter} \ 15$$

$$ \ G \ \underrightarrow{7 \ letter} \ 7 $$

$$ \ H \ \underrightarrow{8 \ letter} \ 8$$

$$ \ U \ \underrightarrow{21 \ letter} \ 21$$

$$ \ R \ \underrightarrow{18 \ letter} \ 18$$

$$ \ T \ \underrightarrow{20 \ letter} \ 20$$

Similarly,

$$ \ D \ \underrightarrow{4 \ letter} \ 4$$

$$ \ E \ \underrightarrow{5 \ letter} \ 5$$

$$ \ V \ \underrightarrow{22 \ letter} \ 22 $$

$$ \ E \ \underrightarrow{5 \ letter} \ 5$$

$$ \ L \ \underrightarrow{12 \ letter} \ 12$$

$$ \ O \ \underrightarrow{15 \ letter} \ 15$$

$$ \ P \ \underrightarrow{16 \ letter} \ 16$$

Hence, the required number will be 45225121516.