Abstract: The evolution of modern programming languages has shifted from merely pursuing syntactic features to systematically coordinating language design with toolchain development. This article takes MoonBit as a case study to systematically elucidate how modern programming languages establish a balance between theoretical innovation and engineering practice. At the language feature design level, MoonBit addresses core scenarios including data processing, control flow ion, error handling, and concurrent programming. Through feature designs oriented toward real engineering problems, it provides practical value while maintaining language simplicity, embodying systematic thinking from theoretical elegance to engineering usability. At the toolchain integration level, MoonBit has coordinated the compiler, IDE, and build system as a unified whole from the outset of its design. Through deep integration of compiler and IDE, incremental checking mechanisms, interface file systems, and language-native testing support, it constructs a vertically integrated development environment that significantly reduces engineering friction and cognitive burden. This study demonstrates that the competitiveness of modern programming languages depends not only on the design of language features, but more importantly on the systematic coordination of language design, compiler implementation, and development tools. This systems engineering approach provides important methodological reference for the future development of modern programming languages.