FeynCalcExternal[exp] translates exp from the internal
FeynCalc representation to a shorthand form.
FeynCalcExternal[DiracGamma[5]]\bar{\gamma }^5
FeynCalcExternal[DiracGamma[5]] // StandardForm
(*GA[5]*)ex = {GA[\[Mu]], GAD[\[Rho]], GS[p], SP[p, q], MT[\[Alpha], \[Beta]], FV[p, \[Mu]]}\left\{\bar{\gamma }^{\mu },\gamma ^{\rho },\bar{\gamma }\cdot \overline{p},\overline{p}\cdot \overline{q},\bar{g}^{\alpha \beta },\overline{p}^{\mu }\right\}
ex // StandardForm
(*{GA[\[Mu]], GAD[\[Rho]], GS[p], SP[p, q], MT[\[Alpha], \[Beta]], FV[p, \[Mu]]}*)ex // FeynCalcInternal\left\{\bar{\gamma }^{\mu },\gamma ^{\rho },\bar{\gamma }\cdot \overline{p},\overline{p}\cdot \overline{q},\bar{g}^{\alpha \beta },\overline{p}^{\mu }\right\}
ex // FeynCalcInternal // StandardForm
(*{DiracGamma[LorentzIndex[\[Mu]]], DiracGamma[LorentzIndex[\[Rho], D], D], DiracGamma[Momentum[p]], Pair[Momentum[p], Momentum[q]], Pair[LorentzIndex[\[Alpha]], LorentzIndex[\[Beta]]], Pair[LorentzIndex[\[Mu]], Momentum[p]]}*)ex // FeynCalcInternal // FeynCalcExternal // StandardForm
(*{GA[\[Mu]], GAD[\[Rho]], GS[p], SP[p, q], MT[\[Alpha], \[Beta]], FV[p, \[Mu]]}*)