In international curricula such as A-Level and AP

English-medium instruction (EMI) is often regarded as the "gold standard" for academic success. The "English-only" policies adopted in these contexts are frequently premised on the traditional assumption that first language use impedes second language acquisition. However

such monolingual ideologies overlook a cognitive reality: learning exclusively through a weaker language imposes a heavy cognitive load. This study adopts a qualitative case study approach

conducting semi-structured interviews with eight students transitioning from Grade 10 to Grade 11 in A-Level/AP programmes. The findings reveal three strategic mechanisms employed by learners: first

conceptual anchoring

presenting as a four-tier dynamic spectrum evolving from lexical segmentation to bilingual integration; second

strategic monolingualisation

whereby learners actively suppress their L1 based on the availability of cognitive resources

forming a continuum of intensity; third

legitimising buffers

through which learners deploy discursive strategies—such as the "ibuprofen metaphor" (framing L1 use as an emergency resource) and "contextual differentiation"—to navigate institutional pressures. A notable finding is the "discourse-practice divide

" which challenges language attitude research that relies solely on self-report measures. This study argues for a shift in international curriculum language policy from rigid monolingual restrictions to dynamic accommodation

recognising the cognitive value of learners' full linguistic repertoires. Furthermore

it offers new insights for curriculum design in international programmes that currently prioritise monolingual policies—at the epistemological level

reserving space for L1-supported conceptual understanding during the preview phase; at the cognitive level

encouraging students to strategically mobilise bilingual resources based on cognitive load and English proficiency; at the institutional level

relaxing the singular pursuit of English-only instruction and legitimising L1 mobilisation within bilingual resource deployment

thereby reducing learners' psychological burden when drawing on their first language.