Help Me Type on My New Keyboard

Question

Overview

As most of y'all who visit chat know, I am Russian by ethnicity^{[citation not needed]}. Recently, I switched from a keyboard that maps the letters 1-to-1 (mnemonic) to Windows' default mnemonic keyboard. Here are the letter mappings:

"`" -> "ъ"
"q" -> "я"
"w" -> "ш"
"e" -> "е"
"r" -> "р"
"t" -> "т"
"u" -> "у"
"i" -> "и"
"o" -> "о"
"p" -> "п"
"a" -> "а"
"d" -> "д"
"f" -> "ф"
"g" -> "г"
"h" -> "х"
"k" -> "к"
"l" -> "л"
"'" -> "ь"
"z" -> "з"
"x" -> "ж"
"v" -> "в"
"b" -> "б"
"n" -> "н"
"m" -> "м"

You may have notcied that s, c, y, and j are missing. This keyboard, unlike the first one I used, has several combining keys (the aforementioned ones) These keys, while also having their own letters mapped to them, can be combined with other keys in sequence to write even more letters. The combinations for those keys are as follows:

"sc" -> "щ"
"ch" -> "ч"
"ya" -> "я"
"ye" -> "э"
"yo" -> "ё"
"yu" -> "ю"
"ja" -> "я"
"je" -> "э"
"jo" -> "ё"
"ju" -> "ю"

Note that there are 3 ways to write я: q, ya, and ja.

To type the single letters mapped to them, either press that key and then press space, or type an unrecognised key combination. Here are the single letter mappings for those keys:

"s" -> "с"
"c" -> "ц"
"y" -> "ы"
"j" -> "й"

For example, if I type in c (note the space), it will give me ц, while typing in cy gives me цы. Typing in yosc is ёщ, and yq is ыя.

The task

Your input will be given as all lowercase Russian + ASCII space, and you task is to convert that to a sequence of letters in the US keyboard I'd have to type.

Testcases

"один" (one) -> "odin"
"стапятидесятитрёхтысячный" (one hundered fifty three thousandth) ->  "stapqtidesqtitryohtysqchnyj" or "stapyatidesyatitryohtysjachnyj" or any variation on the typing of "я" or "ё" 
"код гольф" (code golf) -> "kod gol'f"
"иван рубит дрова вова топит печь" (Ivan is splitting wood, Vova is stoking the stove; a common mnemonic for the six noun cases) -> "ivan rubit drova vova topit pech'"
"разъяренный чтец эгоистично бьёт пятью жердями шустрого фехтовальщика" (An enraged narrator selfishly beats with five poles a nimble fencer; a sentence that uses all 33 Russian letters) -> "raz`yarennyj chtec  jegoistichno b'yot pqt'yu xerdyami wustrogo fehtoval'scika" (note the double space after "chtec". I used a mixture of "q" and "ya" for "я" here)

Scoring

As this is code-golf, shortest answer in bytes wins.

Answer 1

JavaScript (ES6), 106 bytes

s=>s.replace(/\S/g,c=>"rs tufhc chwsc`y 'yeyuq_yoabvgdexzij klmnop".match(/[scyj]?./g)[c.charCodeAt()%34])

Try it online!

Answer 2

Retina 0.8.2, 159 bytes

щ
sc
ч
ch
ё
yo
ю
yu
э
je
ю
ju
T`сцыы`scyj`с[^ scyjц]|ц[^ scyjх]|[йы][^ scyjаеоу]
[сцыы]
$& 
T`а-цшъ-ья`abvg\dexzi-pr-uf\hc\w\`y'q

Try it online! Link includes test cases. Explanation:

щ
sc
ч
ch
ё
yo
ю
yu
э
je
ю
ju

Translate the digraphs.

T`сцыы`scyj`с[^ scyjц]|ц[^ scyjх]|[йы][^ scyjаеоу]

Transliterate any unrecognised pairs starting with s, c, y or j.

[сцыы]
$& 

Insert spaces after any other letter that maps to s, c, y or j.

T`а-цшъ-ья`abvg\dexzi-pr-uf\hc\w\`y'q

Transliterate the rest of the Russian letters.

Answer 3

Python, 125 bytes

lambda s:re.sub('\S',lambda c:re.findall("[scyj]?.","rs tufhc chwsc`y 'yeyuq_yoabvgdexzij klmnop")[ord(c[0])%34],s)
import re

Attempt This Online!

Port of Arnauld's JS answer.