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Extremely metal-deficient (XMD) comma compact and low-mass star-forming galaxies (SFGs) at low redshifts are considered to be the likely nearby counterparts of the high-z star-forming dwarf galaxies thought to be responsible for the reionization of the Universe. We propose to observe with the HST-COS a complete sample of the nine most metal-deficient (12+logO-H<7.25) compact SFGs known in the local universe comma to obtain medium-resolution spectra of the Ly-alpha emission line. Only one galaxy with such a low metallicity comma I Zw 18 comma has been studied previously with the HST-COS. These SFGs were selected from the Data Release 16 and earlier releases of the Sloan Digital Sky Survey to be not only XMD comma but also to be very compact and to have very young starbursts (EW(Hbeta)>100A). Among them one galaxy comma J0811+4730 with 12+logO-H = 6.98 comma is one of the lowest-metallicity low-z SFG known to date. The Ly-alpha profiles in those medium resolution spectra will be used to indirectly estimate the escape fraction of the Lyman continuum and will provide important insight on the ISM and radiation field of the star-forming regions. Obtaining the rest-UV spectra of these nine XMD SFGs which will serve as templates for the analysis of spectra of high-z dwarf galaxies with active star formation comma is thus both urgent and crucial for upcoming studies with the JWST and the largest ground-based facilities.