Is the translation of Qur'an 4:40 "If there be a good deed, He will repay twofold" inaccurate?

Question

The translation of the Qur'an by Maulana Wahiduddin Khan contains:

God does not wrong anyone by as much as a grains weight. If there be a good deed, He will repay twofold, and will bestow out of His own bounty an immense reward. -- Qur'an 4:40 (translation available from Islam Awakened)

I'm skeptical at the word "twofold" here in particular, and I see that other translations do not use that word. I want to check if this specific numerical increase (a factor of two) in good deeds is supported (or even partially implied) by the Arabic text.

Question: Is the translation of Qur'an 4:40 "If there be a good deed, He will repay twofold" inaccurate?

Tafsir suggest it's a "doubling", but it's still not clear:

(He will double it) from one to ten times (and will give (the doer) from His presence an immense reward) an abundant reward in Paradise. -- Tanwîr al-Miqbâs min Tafsîr Ibn ‘Abbâs

...and if it be a good deed, He will double it, and it cannot be a good deed unless it is [done] for Him -- Kashani Tafsir

...if it be a good deed, He will double it and give from Himself a great wage. -- Al Qushairi Tafsir

Answer 1

The translation is indeed inaccurate. The verse says:

إِنَّ اللَّهَ لَا يَظْلِمُ مِثْقَالَ ذَرَّةٍ وَإِن تَكُ حَسَنَةً يُضَاعِفْهَا وَيُؤْتِ مِن لَّدُنْهُ أَجْرًا عَظِيمًا

The Arabic word يُضَاعِفْهَا means multiply. It is not restricted to two-fold or double, but can be used to describe any multiplier.

Islamically, in al-Baqarah 2:261, one can see that Allah uses the same word to describe 700 times the reward. In Sahih Muslim 1151 e, the same word is used to describe 10-700 folds.

Lingguistically, the word ضِعْفُ on its own is commonly used to describe double, but is not restricted to only twofold, albeit the most commonly understood meaning (as in Lesan al-Arab):

وقال الزجاج: ضِعْفُ الشيء مِثْلُه الذي يُضَعِّفُه، وأَضْعافُه أَمثالُه

Al-Zajjaj said: di'f means double, our multiples.

Answer 2

Reading from the dictionary meaning here

ضاعف العددَ جعله ضعفين ( مثلين ) أو أكثر

it will be doubled or more

Or at another line it says:

زادها

increase

So from what I can see it means 2X or more.

The translation provided on Quran.com also says:

"He multiplies it and gives from Himself a great reward."