  We present JWST and ALMA results for the lensing system SPT0418-47, which
includes a strongly-lensed, dusty star-forming galaxy at redshift z=4.225 and
an associated multiply-imaged companion. JWST NIRCam and MIRI imaging
observations presented in this paper were acquired as part of the Early Release
Science program Targeting Extremely Magnified Panchromatic Lensed Arcs and
Their Extended Star Formation (TEMPLATES). This data set provides robust,
mutiwavelength detection of stellar light in both the main (SPT0418A) and
companion (SPT0418B) galaxies, while the ALMA detection of [C II] emission
confirms that SPT0418B lies at the same redshift as SPT0418A. From a source
plane reconstruction, we infer that the projected physical separation of the
two galaxies is $4.42\pm 0.05$ kpc. We derive total magnifications of
$\mu=29.5\pm1.2$ and $\mu=4.2\pm 0.9$ for SPT0418A and SPT0418B, respectively.
We use both CIGALE and PROSPECTOR to derive stellar masses. The stellar mass
ratio of SPT0418A and SPT0418B is approximately 4 to 1 ($4.5\pm 1.0$ for CIGALE
and $4.2^{+1.9}_{-1.6}$ for PROSPECTOR). We also see evidence of extended
structure associated with SPT0418A in the lensing reconstruction that is
suggestive of a tidal feature. Interestingly, the star formation rates and
stellar masses of both galaxies are consistent with the main sequence of
star-forming galaxies at this epoch, indicating that this ongoing interaction
has not noticeably elevated the star formation levels.
