Bug#853917: ttx and grep result for DroidSansFallback(Full)?.ttf
Using DroidSansFallback.ttf seems to be the smallest-sized way. I
prefer this. :)
Or the stripped Android version of NanumGothic could be used instead
of the full version in fonts-nanum. It also provides better looking
Korean glyphs than the Droid font but it will still add ~1.25MB.
BTW, current Android (since 6.0) doesn't use NanumGothic but uses Noto Sans CJK.