Extreme emission-line galaxies (EELGs) at redshift z = 1 − 2 provide a unique view of metal-poor, starburst sources that are the likely drivers of the cosmic reionization at z ≥ 6. However, the molecular gas reservoirs of EELGs -the fuel for their intense star-formation -remain beyond the reach of current facilities. We present ALMA [C II] and PdBI CO(2-1) observations of a z = 1.8, strongly lensed EELG SL2S 0217, a bright Lymanα emitter with a metallicity 0.05 Z . We obtain a tentative (∼3-4σ) detection of the [C II] line and set an upper limit on the [C II]/SFR ratio of ≤ 1 × 10 6 L /(M yr −1 ), based on the synthesized images and visibilityplane analysis. The CO(2-1) emission is not detected. Photoionization modelling indicates that up to 80% of the [C II] emission originates from neutral or molecular gas, although we can not rule out that the gas is fully ionized. The very faint [C II] emission is in line with both nearby metal-poor dwarfs and high-redshift Lyman α emitters, and predictions from hydrodynamical simulations. However, the [C II] line is 30× fainter than predicted by the De Looze et al. ( 2014) [C II]-SFR relation for local dwarfs, illustrating the danger of extrapolating locally-calibrated relations to high-redshift, metal-poor galaxies.