This article introduces a novel diacritic-based system for encoding English pronunciation without altering standard orthography. By employing diacritical marks, the system preserves full compatibility with conventional spelling while presenting pronunciation in a clear and systematic manner. The goal of the proposed ELF Diacritic Notation is to provide pronunciation guidance sufficient for international communication, taking into account the principles of English as a Lingua Franca (ELF), particularly the Lingua Franca Core (LFC). It is intended primarily for communication among non-native speakers, supporting intelligible reading and clear pronunciation while helping readers avoid automatic native-language habits and guiding them toward proper English sound production. The system is also suitable for learners and is particularly well suited to independent learners in its extended version, as it can present both spelling and American or British pronunciation in a unified “two-in-one” format. This dual-function notation guides articulation while reinforcing spelling patterns, making it a practical tool for self-study materials and pedagogical texts. The article provides detailed rules for the notation and includes comprehensive guidelines and illustrative examples, demonstrating that the proposed system is both feasible and useful. An example of the practical use of this notation is the summary of this article, which is written using diacritical marks.