With the dollar in steep decline against major Asian currencies including the yen, China's yuan — which effectively maintains a dollar peg — has become undervalued.
Literal
Dollar [subject-が] yen [object-を] starting-with major Asian currencies [against-に対して] sharply-falling [midst-なか], effectively dollar-peg policy [object-を] adopting China [possessive-の] yuan [topic-は] cheap [result-となっている].
Dense financial reporting. をはじめとする 'starting with, including' lists the yen as the leading example among Asian currencies. ドルペッグ政策 'dollar-peg policy' mixes English loanword and Japanese. 割安 'undervalued, cheap relative to what it should be' is a financial term. Multiple relative clauses and stacked modifiers make this structurally demanding.